ipsec6_process_packet is called before ip6_output fixes ip6_plen.
Update ip6_plen before bpf processing to be able see correct value.

MFC after:	1 week
Sponsored by:	Yandex LLC


git-svn-id: svn+ssh://svn.freebsd.org/base/head@274454 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f
We don't return sp pointer, thus NULL assignment isn't needed.
And reference to sp will be freed at the end.

MFC after:	1 week
Sponsored by:	Yandex LLC


git-svn-id: svn+ssh://svn.freebsd.org/base/head@274455 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f