Do not assert buffer lock in VFS_STRATEGY() when kernel already paniced.

Sponsored by:	The FreeBSD Foundation
MFC after:	1 week

sys/kern/vfs_subr.c

@@ -3894,7 +3894,7 @@ vop_strategy_pre(void *ap)
 	if ((bp->b_flags & B_CLUSTER) != 0)
 		return;
 
-	if (!BUF_ISLOCKED(bp)) {
+	if (panicstr == NULL && !BUF_ISLOCKED(bp)) {
 		if (vfs_badlock_print)
 			printf(
 			    "VOP_STRATEGY: bp is not locked but should be\n");