Change unicast connection of DHCPv4 client as a raw socket

[yaocw2020]

If the network manager in the operating system uses DHCP to obtain an IP for the network card, it will occupy the DHCP client port. In this case the release function will fail because the unicast connection with UDP socket need the same port. Use a raw udp socket instead of a datagram udp socket to solve it.

Signed-off-by: yaocw2020 [email protected]

[codecov[bot]]

Codecov Report

Merging #458 (28832bb) into master (3c283ff) will decrease coverage by 0.34%. The diff coverage is 14.28%.

@@            Coverage Diff             @@
##           master     #458      +/-   ##
==========================================
- Coverage   67.42%   67.08%   -0.35%     
==========================================
  Files          90       90              
  Lines        3758     3795      +37     
==========================================
+ Hits         2534     2546      +12     
- Misses       1053     1076      +23     
- Partials      171      173       +2     

Flag	Coverage Δ
integtests	?
unittests	67.08% <14.28%> (-0.35%)	:arrow_down:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
dhcpv4/nclient4/client.go	59.59% <0.00%> (+1.18%)	:arrow_up:
dhcpv4/nclient4/conn_unix.go	39.75% <15.15%> (-15.15%)	:arrow_down:
dhcpv6/ztpv6/parse_vendor_options.go	89.74% <0.00%> (-3.59%)	:arrow_down:

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[yaocw2020]

@insomniacslk @pmazzini @hugelgupf Could you help review this pr? Moreover, are the unit tests mandatory? It seems hard to add the unit tests for the arp request in this testing environment.

[yaocw2020]

@insomniacslk @pmazzini @hugelgupf Could you help review this pr? By the way, there is something abnormal about the integration-tests(dhcpv6)