sockets for IPv6 raw sockets: separately lock the inpcb for determining
the destination address for a connect()'d raw socket at the rip6_send()
layer, and then re-acquire the inpcb lock in the rip6_output() layer to
query other options on the socket. Previously, the global raw IP socket
lock was used, which while correct and marginally more consistent, could
add significantly to global raw IP socket lock contention.
MFC after: 1 week
2209e8f159