webadmin: Vnics statistics are not shown for VM unless VNIC is selected

When the subtab is opened, the first VNIC will be auto-selected,
so that its statistics is shown.

Change-Id: I6fbb3ed760bbd6cf2821073a688b7bdda85aa064
Bug-Url: https://bugzilla.redhat.com/915778
Signed-off-by: Alona Kaplan <alkaplan@redhat.com>