async_rcvd: Move MSGF_DONE test under async rcvd spinlock

This flag is meant to be protected by the async rcvd spinlock; use
ssleep instead of tsleep if race happened.

Sysctl node kern.ipc.async_rcvd_drop_race is added to count the
number of async rcvd message dropping races.
async_rcvd: Don't add/drop socket reference on hot path

Instead, add reference in tcp_attach(), and drop the reference in
tcp_close()
libc/sl_find: sync prototype with NetBSD

The sl_find function does not modify the 'name' argument.
Set the constant qualifier on it to match NetBSD.  FreeBSD will make this
change in the future as well.

Submitted by: Eitan Eadler <eadler@freebsd.org>
bnx: Add support for BCM5762 chips

Taken-from: tg3
bpf - Remove crit_enter/exit calls.

bpf_token is used to protect the code now, critical sections are no
longer needed.

Pointed-out-by: sephe