K 10
svn:author
V 2
bz
K 8
svn:date
V 27
2019-11-15T21:51:43.333603Z
K 7
svn:log
V 378
IP6_EXTHDR_CHECK(): remove the last instances

While r354748 removed almost all IP6_EXTHDR_CHECK() calls, these
are not part of the PULLDOWN_TESTS.
Equally convert these IP6_EXTHDR_CHECK()s here to m_pullup() and remove
the extra check and m_pullup() in tcp_input() under isipv6 given
tcp6_input() has done exactly that pullup already.

MFC after:	8 weeks
Sponsored by:	Netflix

END