conncheck: NOMINATION STUN attribute support

Attribute is proposed here: https://tools.ietf.org/html/draft-thatcher-ice-renomination-00
WebRTC supports this attribute: controlling side provides attribute value increased by one each time selected pair is changed:
https://chromium.googlesource.com/external/webrtc/+/3c7d599750405bc734e1d5adbf1b54265b725a9d/p2p/base/p2ptransportchannel.cc#1821
6 jobs for renomination_support in 3 minutes and 58 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #289126
build autotools

00:00:56

passed #289127
build meson

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  Test
passed #289129
distcheck autotools

00:03:01

passed #289131
doc-and-install meson

00:00:38

passed #289128
test autotools

00:01:36

passed #289130
allowed to fail
test meson

00:00:54