Stop using KERNEL_LOCK to protect the per process kqueue list

Stop using KERNEL_LOCK to protect the per process kqueue list

Instead of the KERNEL_LOCK use the ps_mtx for most operations.
If the ps_klist is modified an additional global rwlock (kqueue_ps_list_lock)
is required. This includes the knotes with NOTE_FORK and NOTE_EXIT since
in either cases a ps_klist is changed. In the NOTE_FORK | NOTE_TRACK case
the call to kqueue_register() can sleep this is why a global rwlock is used.

Adjust the reaper() to call knote_processexit() without KERNEL_LOCK.
Double lock idea from visa@
OK mvs@