audit: reduce scope of audit_net_id

audit_net_id isn't used outside kernel/audit.c.  Reduce its scope.

Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
diff --git a/kernel/audit.c b/kernel/audit.c
index 3ef2e0e..9a951e6 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -126,7 +126,7 @@
 
 /* The netlink socket. */
 static struct sock *audit_sock;
-int audit_net_id;
+static int audit_net_id;
 
 /* Hash for inode-based rules */
 struct list_head audit_inode_hash[AUDIT_INODE_BUCKETS];