ovs-router: Fix potential integer overflow.

There was a theoretical (but unlikely to happen in practice) integer
overflow in ovs_router_rule_add_cmd() in the case when rule list
comprised only of rules with priority zero, the new rule priority would
be calculated as UINT_MAX.

Coverity issue:
    CID 556927:         Integer handling issues  (INTEGER_OVERFLOW)
    Expression "rule->prio - 1U", where "rule->prio" is known to be
    equal to 0, under-flows the type of "rule->prio - 1U", which is
    type "unsigned int".

Fixes: e2a2415 ("ovs-router: Introduce ovs/route/rule/{add, del} commands.")
Signed-off-by: Dima Chumak <dchumak@nvidia.com>
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>

Author: chumakd

lib/ovs-router.c

@@ -1030,8 +1030,7 @@ ovs_router_rule_add_cmd(struct unixctl_conn *conn, int argc OVS_UNUSED,
         uint32_t prev_prio = 0;
 
         PVECTOR_FOR_EACH (rule, &rules) {
-            if ((!prio && rule->prio) ||
-                (rule->prio - prev_prio > 1)) {
+            if (rule->prio && (!prio || (rule->prio - prev_prio > 1))) {
                 prio = rule->prio - 1;
             }
             prev_prio = rule->prio;