net, stability: Wait for client VM iface

client_server_active_connection only waited for the server
VM's secondary interface to get its DHCP-assigned IP.
If the client VM's DHCP hadn't completed yet, iperf3 had no
route to the server and exited immediately, causing
_ensure_is_running to time out.

The change will fix
test_tcp_connectivity_between_vms_with_localnet_ipam_nic
failures on CI.

Signed-off-by: Asia Khromov <azhivovk@redhat.com>

Author: azhivovk

libs/net/traffic_generator.py

@@ -265,6 +265,7 @@ def client_server_active_connection(
         Traffic runs with infinite duration until context exits.
     """
     server_ip = str(lookup_iface_status_ip(vm=server_vm, iface_name=spec_logical_network, ip_family=ip_family))
+    lookup_iface_status_ip(vm=client_vm, iface_name=spec_logical_network, ip_family=ip_family)
     with TcpServer(vm=server_vm, port=port, bind_ip=server_ip) as server:
         with VMTcpClient(
             vm=client_vm,