[csl] update CSL Channel TLV process to allow for unspecified case

[abtink]

This commit updates how unspecified CSL channel is conveyed in MLE messages. Special value of zero in CSL Channel TLV is used to indicate that the CSL channel is unspecified. The exclusion of the TLV keeps the CSL channel as before (no change to the previously set CSL channel).

---

• This PR contains commit from https://github.com/openthread/openthread/pull/8004.
• This is related to SPEC-1095.
• FYI: @Irving-cl

[size-report[bot]]

Size Report of OpenThread

Merging #8005 into main(9f451a2b325718579cd1a1a398264a1a410dd1a3).

name	branch	text	data	bss	total
ot-cli-ftd_1.1	main	462504	780	60772	524056
	#8005	462504	780	60772	524056
	+/-	0	0	0	0
ot-cli-mtd_1.1	main	381880	780	50564	433224
	#8005	381880	780	50564	433224
	+/-	0	0	0	0
ot-ncp-ftd_1.1	main	444228	780	59752	504760
	#8005	444228	780	59752	504760
	+/-	0	0	0	0
ot-ncp-mtd_1.1	main	366364	780	49544	416688
	#8005	366364	780	49544	416688
	+/-	0	0	0	0
ot-rcp_1.1	main	58136	564	19964	78664
	#8005	58136	564	19964	78664
	+/-	0	0	0	0
libopenthread-cli-ftd.a_1.1	main	45925	0	4244	50169
	#8005	45925	0	4244	50169
	+/-	0	0	0	0
libopenthread-cli-mtd.a_1.1	main	38548	0	4244	42792
	#8005	38548	0	4244	42792
	+/-	0	0	0	0
libopenthread-ftd.a_1.1	main	242866	20	39090	281976
	#8005	242858	20	39090	281968
	+/-	-8	0	0	-8
libopenthread-mtd.a_1.1	main	175908	20	28882	204810
	#8005	175908	20	28882	204810
	+/-	0	0	0	0
libopenthread-ncp-ftd.a_1.1	main	31597	0	5852	37449
	#8005	31597	0	5852	37449
	+/-	0	0	0	0
libopenthread-ncp-mtd.a_1.1	main	26441	0	5852	32293
	#8005	26441	0	5852	32293
	+/-	0	0	0	0
libopenthread-rcp.a_1.1	main	8894	0	4988	13882
	#8005	8894	0	4988	13882
	+/-	0	0	0	0
libopenthread-radio.a_1.1	main	15939	0	174	16113
	#8005	15939	0	174	16113
	+/-	0	0	0	0
ot-cli-ftd_1.3	main	485288	780	70468	556536
	#8005	485272	780	70468	556520
	+/-	-16	0	0	-16
ot-cli-mtd_1.3	main	397048	780	51820	449648
	#8005	397048	780	51820	449648
	+/-	0	0	0	0
ot-ncp-ftd_1.3	main	465972	780	69440	536192
	#8005	465956	780	69440	536176
	+/-	-16	0	0	-16
ot-ncp-mtd_1.3	main	380100	780	50792	431672
	#8005	380100	780	50792	431672
	+/-	0	0	0	0
ot-rcp_1.3	main	60464	564	20532	81560
	#8005	60464	564	20532	81560
	+/-	0	0	0	0
libopenthread-cli-ftd.a_1.3	main	48783	0	4244	53027
	#8005	48783	0	4244	53027
	+/-	0	0	0	0
libopenthread-cli-mtd.a_1.3	main	40812	0	4244	45056
	#8005	40812	0	4244	45056
	+/-	0	0	0	0
libopenthread-ftd.a_1.3	main	261802	20	48242	310064
	#8005	261786	20	48242	310048
	+/-	-16	0	0	-16
libopenthread-mtd.a_1.3	main	187751	20	29594	217365
	#8005	187743	20	29594	217357
	+/-	-8	0	0	-8
libopenthread-ncp-ftd.a_1.3	main	33427	0	5852	39279
	#8005	33427	0	5852	39279
	+/-	0	0	0	0
libopenthread-ncp-mtd.a_1.3	main	27807	0	5852	33659
	#8005	27807	0	5852	33659
	+/-	0	0	0	0
libopenthread-rcp.a_1.3	main	9060	0	4988	14048
	#8005	9060	0	4988	14048
	+/-	0	0	0	0
libopenthread-radio.a_1.3	main	16819	0	206	17025
	#8005	16819	0	206	17025
	+/-	0	0	0	0

[codecov[bot]]

Codecov Report

Merging #8005 (5ac02ed) into main (9f451a2) will increase coverage by 0.00%. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #8005   +/-   ##
=======================================
  Coverage   85.35%   85.36%           
=======================================
  Files         509      509           
  Lines       70759    70754    -5     
=======================================
+ Hits        60399    60401    +2     
+ Misses      10360    10353    -7     

Impacted Files	Coverage Δ
src/core/thread/mle_router.cpp	85.66% <ø> (+0.07%)	:arrow_up:
src/core/thread/mle.cpp	89.51% <100.00%> (-0.06%)	:arrow_down:
src/core/utils/channel_manager.cpp	78.61% <0.00%> (-2.32%)	:arrow_down:
src/core/thread/mesh_forwarder_ftd.cpp	83.77% <0.00%> (-1.98%)	:arrow_down:
src/core/net/dns_client.cpp	79.58% <0.00%> (-1.84%)	:arrow_down:
src/core/mac/data_poll_handler.cpp	83.44% <0.00%> (-1.38%)	:arrow_down:
src/core/backbone_router/bbr_local.cpp	88.11% <0.00%> (-1.23%)	:arrow_down:
src/core/thread/indirect_sender.cpp	90.63% <0.00%> (-0.86%)	:arrow_down:
src/core/thread/mesh_forwarder.cpp	87.34% <0.00%> (-0.61%)	:arrow_down:
src/core/meshcop/joiner_router.cpp	88.61% <0.00%> (-0.50%)	:arrow_down:
... and 22 more