test: Wait for network before starting passt in two_guests setup

As pasta now configures that target network namespace with
--config-net, we need to wait for addresses and routes to be actually
present. Just sending netlink messages doesn't mean this is done
synchronously.

A more elegant alternative, which probably makes sense regardless of
this test setup, would be to query, from pasta, addresses and routes
we added, and wait until they're there, before proceeding.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

test/lib/setup

@@ -208,6 +208,8 @@ setup_two_guests() {
 
 	__ifname="$(context_run qemu_1 "ip -j link show | jq -rM '.[] | select(.link_type == \"ether\").ifname'")"
 
+	sleep 1
+
 	__opts=
 	[ ${PCAP} -eq 1 ] && __opts="${__opts} -p ${LOGDIR}/passt_1.pcap"
 	[ ${DEBUG} -eq 1 ] && __opts="${__opts} -d"