tcp: Avoid unnecessary calling of in_pcbladdr() in tcp_connect()

If in_pcbladdr() was called and inp_laddr was saved, there would be
no need to call in_pcbladdr() again, after the inp was forwarded to
its owner netisr.
net: Add initport protosw method to init socket's default protocol port

Currently only tcp implements this method to distribute pru_attach and
pru_connect workload.

Nuke no longer necessary protosw flag PR_RAND_INITPORT and sysctl
kern.ipc.rand_initport.
systat/ip,tcp: Initialize curstate to avoid overflow/underflow
udp: Fix "unconnect" and cleanup connect

Put udp inpcb into wildcard hash in pru_disconnect method.  This restores
the old behaviour of traditional BSD "unconnect".

Clean up pru_connect after fixing the "unconnect" support; in preparation
for distributing udp inpcb across netisrs.
ip/demux: Remove no longer applied comment
tcp: White space cleanup; no functional changes.
uipc: Nuke unnecessary void cast
uipc: Fix comment
socket: {soabort,so_pru_abort}a -> {soabort,so_pru_abort}_async

No functional change.  They are consistent w/ other so and so_pru
function names.
socket: so_pru_abort_oncpu -> so_pru_abort_direct

No functional change.  It is consistent w/ other so_pru functions name.