tst_net.sh: Detect IPv6 disabled

[pevik]

We should TCONF in tst_net.sh when Operation not supported.

Testing ping02.sh -6:

ping02 1 TINFO: initialize 'lhost' 'ltp_ns_veth2' interface
ping02 1 TINFO: add local addr 10.0.0.2/24
ping02 1 TINFO: add local addr fd00:1:1:1::2/64
RTNETLINK answers: Operation not supported
ping02 1 TINFO: initialize 'rhost' 'ltp_ns_veth1' interface
ping02 1 TINFO: add remote addr 10.0.0.1/24
ping02 1 TINFO: add remote addr fd00:1:1:1::1/64
RTNETLINK answers: Operation not supported
# tst_net_iface_prefix.c:133: TINFO: prefix and interface not found for 'fd00:1:1:1::2'.

ping02 1 TINFO: Network config (local -- remote):
ping02 1 TINFO: ltp_ns_veth2 -- ltp_ns_veth1
ping02 1 TINFO: 10.0.0.2/24 -- 10.0.0.1/24
ping02 1 TINFO: fd00:1:1:1::2/64 -- fd00:1:1:1::1/64
ping02 1 TINFO: timeout per run is 0h 5m 0s
ping6: socket: Address family not supported by protocol
ping02 1 TFAIL: ping6 -I ltp_ns_veth2 -c 3 -s 8 -f -p 000102030405060708090a0b0c0d0e0f fd00:1:1:1::1 >/dev/null failed unexpectedly

Also nfs_lib.sh does not support it (probably fixing tst_net.sh should be enough to fix it), see: https://lists.linux.it/pipermail/ltp/2021-May/022858.html

[pevik]

Patch v2 sent: https://patchwork.ozlabs.org/project/ltp/list/?series=299318&state=*

[pevik]

Fixes were applied some time ago, but there are more fixes in the queue: https://patchwork.ozlabs.org/project/ltp/patch/[email protected]/

But this must be rewritten: https://patchwork.ozlabs.org/project/ltp/patch/[email protected]/

[pevik]

Updated patchset: https://patchwork.ozlabs.org/project/ltp/list/?series=342539&state=*