Add kern/kern_sysctl.c.
add task fields to socket
create sosplice task queue
implement sotask()
add and del sosplice task
check for so_splice in sotask()
Put sosplice_taskq into #ifdef SOCKET_SPLICE.
call yield() to avoid user land starvation
do not use task_add() if PR_WANTRCVD
Do not cast somove() to void.
Add a comment explaining why we use the sosplice thread.
Merge branch 'sosplice-thread' of github.com:bluhm/sys into sosplice-thread