util_sd: fix incorrect strings match

util_sd: fix incorrect strings match

parse_ace() accepted strings like "ALLOWED123" as valid ACE
types because strncmp() compared only prefixes without
NULL terminators.

Switch to exact string comparison to ensure only valid
ACE type names are accepted.

Pair-Programmed-With: Dmitry Mikhalchenko <tascad@altlinux.org>
Signed-off-by: Daniil Sarafannikov <sarafannikovda@sgu.ru>
Reviewed-by: Anoop C S <anoopcs@samba.org>
Reviewed-by: Gary Lockyer <gary@catalyst.net.nz>
Autobuild-User(master): Anoop C S <anoopcs@samba.org>
Autobuild-Date(master): Wed Jun  3 08:26:04 UTC 2026 on atb-devel-224