Move lock assertions to top of in6_pcbladdr(): we still want them to run

Move lock assertions to top of in6_pcbladdr(): we still want them to run
even if we're going to return an argument-based error.

Assert pcbinfo lock in in6_pcblookup_local(), in6_pcblookup_hash(), since
they walk pcbinfo inpcb lists.

Assert inpcb and pcbinfo locks in in6_pcbsetport(), since
port reservations are changing.

MFC after:	3 months