libapparmor: Migrate aa_features API to openat() style

Instead of only accepting a path in the aa_features API, accept a
directory file descriptor and a path like then openat() family of
syscalls. This type of interface is better since it can operate exactly
like a path-only interface, by passing AT_FDCWD or -1 as the dirfd.
However, using the dirfd/path combination, it can eliminate string
allocations needed to open files in subdirectories along with the
even more important benefits mentioned in the open(2) man page.

Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Acked-by: Seth Arnold <seth.arnold@canonical.com>

parser/parser_main.c

@@ -397,7 +397,7 @@ static int process_arg(int c, char *optarg)
 		}
 		break;
 	case 'M':
-		if (aa_features_new(&features, optarg)) {
+		if (aa_features_new(&features, AT_FDCWD, optarg)) {
 			fprintf(stderr,
 				"Failed to load features from '%s': %m\n",
 				optarg);