src/login_nopam.c: list_match(): Use iteration instead of recursion

src/login_nopam.c: list_match(): Use iteration instead of recursion

The recursive nature of list_match() triggered regression during
refactoring.  In Linux-PAM, the same code exists which could lead to
stack overflow because <access.conf> could be arbitrarily long.

Use an iterative approach for easier refactoring, to support long
lines in the future and to stay in sync with Linux-PAM.

Signed-off-by: Tobias Stoeckmann <tobias@stoeckmann.org>
Reviewed-by: Serge Hallyn <serge@hallyn.com>
Signed-off-by: Alejandro Colomar <alx@kernel.org>