acl: forbid rule with priority zero

acl: forbid rule with priority zero

If user specifies priority=0 for some of ACL rules
that can cause rte_acl_classify to return wrong results.
The reason is that priority zero is used internally for no-match nodes.
See more details at: https://bugs.dpdk.org/show_bug.cgi?id=79.
The simplest way to overcome the issue is just not allow zero
to be a valid priority for the rule.

Fixes: dc276b5780c2 ("acl: new library")
Cc: stable@dpdk.org
Signed-off-by: Konstantin Ananyev <konstantin.ananyev@intel.com>