When doing ARM stack unwinding as part of stack_save(9), do not search

loaded modules (pass 0/false for the can_lock arg).  Searching the unwind
info in modules acquires an exclusive sxlock, and the stack(9) functions can
be called in a context where unbounded sleeps are forbidden (such as from
the witness checkorder code).

Just ignoring the existence of modules in stack_save() is not ideal, so I'm
looking for a better solution, but this commit will make it possible to boot
an ARM kernel with WITNESS enabled again, until I get something better.

PR:		242200

sys/arm/arm/stack_machdep.c

@@ -40,7 +40,7 @@ stack_capture(struct stack *st, struct unwind_state *state)
 {
 
 	stack_zero(st);
-	while (unwind_stack_one(state, 1) == 0) {
+	while (unwind_stack_one(state, 0) == 0) {
 		if (stack_put(st, state->registers[PC]) == -1)
 			break;
 	}