webadmin: Improved boot protocol behavior in host network dialog

It used to be that if the address/subnet/gateway fields were edited,
they would be committed to the VdsNetworkInterface upon pressing OK
even if the chosen boot protocol was for example NONE, in which case
it would be expected that these fields wouldn't be committed. So now
changes are committed only if the chosen boot protocol is IP_STATIC.

Change-Id: I76f3f8d5c3f214927761effa571ca23f2e6c239c
Bug-Url: https://bugzilla.redhat.com/989360
Signed-off-by: Lior Vernia <lvernia@redhat.com>