tcp: Check multicast sopt name after sopt level is checked
inpcb: Revoke INP_WILDCARD_MP, which serves no purpose now

While I'm here, use ncpus2 instead of ncpus for TCP, which only uses
ncpus2 netisrs.
inpcb: Define INP_WASBOUND_NOTANY as protocol specific flag
udp: Optimize detach path

If the inpcb was never put onto wildcard hash and the multicast options
were never accessed nor modified, we could directly dispose the inpcb
on detach path instead of going through all netisrs to make sure that
it is no longer being accessed.

After this commit 'kq_connect_client -u' gives ~180Kconns/s instead of
~160Kconns/s (~12% improvement).