Don't recurse the BPF descriptor lock during the BIOCSDLT operation

(and panic).  To try to finish making BPF safe, at the very least,
the BPF descriptor lock really needs to change into a reader/writer
lock that controls access to "settings," and a mutex that controls
access to the selinfo/knote/callout.  Also, use of callout_drain()
instead of callout_stop() (which is really a much more widespread
issue).

sys/net/bpf.c

@@ -1558,10 +1558,10 @@ bpf_setdlt(d, dlt)
 	}
 	mtx_unlock(&bpf_mtx);
 	if (bp != NULL) {
-		BPFD_LOCK(d);
 		opromisc = d->bd_promisc;
 		bpf_detachd(d);
 		bpf_attachd(d, bp);
+		BPFD_LOCK(d);
 		reset_d(d);
 		BPFD_UNLOCK(d);
 		if (opromisc) {