Make it possible for multiple threads to enter kqueue_scan() in parallel.

This is a requirement to use a sleeping lock inside kqueue filters.
It is now possible, but not recommended, to sleep inside ``f_event''.

Threads iterating over the list of pending events are now recognizing
and skipping other threads' markers.  knote_acquire() and knote_release()
must be used to "own" a knote to make sure no other thread is sleeping
with a reference on it.

Acquire and marker logic taken from DragonFly but the KERNEL_LOCK()
is still serializing the execution of the kqueue code.

This also enable the NET_LOCK() in socket filters.

Tested by abieber@ & juanfra@, run by naddy@ in a bulk, ok visa@, bluhm@

0 files changed, 0 insertions, 0 deletions