system-tests: Wait for all interfaces to have IPv6

The "SNAT in gateway router mode" could occasionally
fail, because the ext1 IPv6 address wasn't ready and
the NA packet arrived too late for the ping to succeed.

Signed-off-by: Ales Musil <amusil@redhat.com>
Acked-by: Mark Michelson <mmichels@redhat.com>
Signed-off-by: Mark Michelson <mmichels@redhat.com>

tests/system-ovn.at

@@ -8691,7 +8691,8 @@ ADD_VETH(ext1, ext1, br0, "172.16.1.1/24", "00:ee:00:01:01:01", \
 check ovn-nbctl --wait=hv sync
 wait_for_ports_up
 OVS_WAIT_UNTIL([test "$(ip netns exec ls1p1 ip a | grep 2001::1 | grep tentative)" = ""])
-OVS_WAIT_UNTIL([test "$(ip netns exec ls1p2 ip a | grep 2002::1 | grep tentative)" = ""])
+OVS_WAIT_UNTIL([test "$(ip netns exec ls1p2 ip a | grep 2002::2 | grep tentative)" = ""])
+OVS_WAIT_UNTIL([test "$(ip netns exec ext1 ip a | grep 1711::1 | grep tentative)" = ""])
 
 NS_CHECK_EXEC([ls1p1], [ping -q -c 3 -i 0.3 -w 2  172.16.1.1 | FORMAT_PING], \
 [0], [dnl