MINOR: connection: Add function to get src/dst without updating the connection

conn_get_src() and conn_get_dst() functions are used to fill the source and
destination addresses of a connection. On success, ->src and ->dst
connection fields can be safely used.

For convenience, 2 new functions are added here: conn_src() and conn_dst().
These functions return the corresponding address, as a const and only if it
is already set. Otherwise NULL is returned.
diff --git a/include/haproxy/connection.h b/include/haproxy/connection.h
index a140aa7..bacf7ca 100644
--- a/include/haproxy/connection.h
+++ b/include/haproxy/connection.h
@@ -407,6 +407,22 @@
 	return cs ? cs->conn : NULL;
 }
 
+/* Returns the source address of the connection or NULL if not set */
+static inline const struct sockaddr_storage *conn_src(struct connection *conn)
+{
+	if (conn->flags & CO_FL_ADDR_FROM_SET)
+		return conn->src;
+	return NULL;
+}
+
+/* Returns the destination address of the connection or NULL if not set */
+static inline const struct sockaddr_storage *conn_dst(struct connection *conn)
+{
+	if (conn->flags & CO_FL_ADDR_TO_SET)
+		return conn->dst;
+	return NULL;
+}
+
 /* Retrieves the connection's original source address. Returns non-zero on
  * success or zero on failure. The operation is only performed once and the
  * address is stored in the connection for future use.