parser: Check kernel stacking support when handling stacked transitions

Check if the current kernel supports stacking. If not, ensure that named
transitions (exec, change_profile, etc.) do not attempt to stack their
targets.

Also, set up the change_profile vector according to whether or not the
kernel supports stacking. Earlier kernels expect the policy namespace to
be in its own NUL-terminated vector element rather than passing the
entire label (namespace and profile name) as a single string to the
kernel.

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

parser/parser_main.c

@@ -638,6 +638,8 @@ static void set_supported_features(void)
 						       "policy/set_load");
 	kernel_supports_diff_encode = aa_features_supports(features,
 							   "policy/diff_encode");
+	kernel_supports_stacking = aa_features_supports(features,
+							"domain/stack");
 
 	if (aa_features_supports(features, "policy/versions/v7"))
 		kernel_abi_version = 7;