restapi: Don't set bootproto on VLAN attach to NIC

Setting the boot protocol on attaching a network to a host's NIC causes
the new VLAN to get the same boot parameters as the NIC itself, which
makes little sense as the VLAN is a different L2 network and it's boot
protocol info should be set accordingly and not automatically.

Change-Id: I78b415592e2bc1a9fea901cadb3ee928f2935a14
Bug-Url: https://bugzilla.redhat.com/980486
Signed-off-by: Mike Kolesnik <mkolesni@redhat.com>