Fix a lockorder reversal I introduced in r193436 when I moved the

mtx_destroy() of the pool mutex to after SVC_RELEASE(), because
the pool mutex was still locked when soclose() was called by svc_dg_destroy().
To fix this, an mtx_unlock() was added where mtx_destroy() was before
r193436.

Reviewed by:	jhb
Tested by:	pho
Approved by:	rwatson (mentor)

Author: Rick Macklem

sys/rpc/svc.c

@@ -174,6 +174,7 @@ svcpool_destroy(SVCPOOL *pool)
 		svc_unreg(pool, s->sc_prog, s->sc_vers);
 		mtx_lock(&pool->sp_lock);
 	}
+	mtx_unlock(&pool->sp_lock);
 
 	TAILQ_FOREACH_SAFE(xprt, &cleanup, xp_link, nxprt) {
 		SVC_RELEASE(xprt);