divert socket fixups:

o pickup Giant in divert_packet to protect sbappendaddr since it

can be entered through MPSAFE callouts or through ip_input when
mpsafenet is 1

o add missing locking on output
o add locking to abort and shutdown
o add a ctlinput handler to invalidate held routing table references

on an ICMP redirect (may not be needed)

Supported by: FreeBSD Foundation