netfilter: nft_set_rbtree: Introduce and use nft_rbtree_interval_start()

Replace negations of nft_rbtree_interval_end() with a new helper,
nft_rbtree_interval_start(), wherever this helps to visualise the
problem at hand, that is, for all the occurrences except for the
comparison against given flags in __nft_rbtree_get().

This gets especially useful in the next patch.

Signed-off-by: Stefano Brivio <[e-mail]>
Signed-off-by: Pablo Neira Ayuso <[e-mail]>

net/netfilter/nft_set_rbtree.c

···
 	       (*nft_set_ext_flags(&rbe->ext) & NFT_SET_ELEM_INTERVAL_END);
 }
 
+static bool nft_rbtree_interval_start(const struct nft_rbtree_elem *rbe)
+{
+	return !nft_rbtree_interval_end(rbe);
+}
+
 static bool nft_rbtree_equal(const struct nft_set *set, const void *this,
 			     const struct nft_rbtree_elem *interval)
 {
···
 			if (interval &&
 			    nft_rbtree_equal(set, this, interval) &&
 			    nft_rbtree_interval_end(rbe) &&
-			    !nft_rbtree_interval_end(interval))
+			    nft_rbtree_interval_start(interval))
 				continue;
 			interval = rbe;
 		} else if (d > 0)
···
 
 	if (set->flags & NFT_SET_INTERVAL && interval != NULL &&
 	    nft_set_elem_active(&interval->ext, genmask) &&
-	    !nft_rbtree_interval_end(interval)) {
+	    nft_rbtree_interval_start(interval)) {
 		*ext = &interval->ext;
 		return true;
 	}
···
 			p = &parent->rb_right;
 		else {
 			if (nft_rbtree_interval_end(rbe) &&
-			    !nft_rbtree_interval_end(new)) {
+			    nft_rbtree_interval_start(new)) {
 				p = &parent->rb_left;
-			} else if (!nft_rbtree_interval_end(rbe) &&
+			} else if (nft_rbtree_interval_start(rbe) &&
 				   nft_rbtree_interval_end(new)) {
 				p = &parent->rb_right;
 			} else if (nft_set_elem_active(&rbe->ext, genmask)) {
···
 			parent = parent->rb_right;
 		else {
 			if (nft_rbtree_interval_end(rbe) &&
-			    !nft_rbtree_interval_end(this)) {
+			    nft_rbtree_interval_start(this)) {
 				parent = parent->rb_left;
 				continue;
-			} else if (!nft_rbtree_interval_end(rbe) &&
+			} else if (nft_rbtree_interval_start(rbe) &&
 				   nft_rbtree_interval_end(this)) {
 				parent = parent->rb_right;
 				continue;