FreeBSD: Create taskq threads in appropriate proc

Stepping stone toward re-enabling spa_thread on FreeBSD.

Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ryan Moeller <ryan@iXsystems.com>
Closes #10715

module/os/freebsd/spl/spl_sysevent.c

@@ -35,6 +35,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/malloc.h>
 #include <sys/kmem.h>
 #include <sys/list.h>
+#include <sys/proc.h>
 #include <sys/sbuf.h>
 #include <sys/nvpair.h>
 #include <sys/sunddi.h>
@@ -256,6 +257,6 @@ sysevent_worker(void *arg __unused)
 void
 ddi_sysevent_init(void)
 {
-	kproc_kthread_add(sysevent_worker, NULL, &zfsproc, NULL, 0, 0,
+	kproc_kthread_add(sysevent_worker, NULL, &system_proc, NULL, 0, 0,
 	    "zfskern", "sysevent");
 }