Allow the use of a stale p_stops value in STOPEVENT(), grabbing the proc lock only if we actually need to perform a stop.  This avoids two locks and unlocks of the process lock each system call, and wins me about 20% on a simply system call test (getuid(), which would otherwise require no locking).  This also has a net improvement of about 10MB/s on some of the SMP bandwidth tests I'm running.
Allow the use of a stale p_stops value in STOPEVENT(), grabbing
the proc lock only if we actually need to perform a stop.  This
avoids two locks and unlocks of the process lock each system call,
and wins me about 20% on a simply system call test (getuid(),
which would otherwise require no locking).  This also has a net
improvement of about 10MB/s on some of the SMP bandwidth tests
I'm running.

Reviewed by:	jhb

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase