parser: ignore feature abi rules

AppArmor 3.0 requires policy to use a feature abi rule for access to
new features. However some policy may start using abi rules even if
they don't have rules that require new features.  This is especially
true for out of tree policy being shipped in other packages.

Add enough support to older releases that the parser will ignore the
abi rule and warn that it is falling back to the apparmor 2.x
technique of using the system abi.

If the profile contains rules that the older parser does not
understand it will fail policy compilation at the unknown rule instead
of the abi rule.

PR: https://gitlab.com/apparmor/apparmor/merge_requests/196
(backported form commit 83df7c4747)
Signed-off-by: John Johansen <john.johansen@canonical.com>
Acked-by: Seth Arnold <seth.arnold@canonical.com>

parser/parser_misc.c

@@ -111,6 +111,7 @@ static struct keyword_table keyword_table[] = {
 	{"trace",		TOK_TRACE},
 	{"tracedby",		TOK_TRACEDBY},
 	{"readby",		TOK_READBY},
+	{"abi",			TOK_ABI},
 
 	/* terminate */
 	{NULL, 0}