Avoid dialog dismiss until IP and proxy is valid

Accepting an invalid configuration can lead to
unexpected behavior.

Validate all fields before dismissing dialog. A further
improvement to this can be highlighting the faulty field
to the user by a color change.

Bug: 3462049
Change-Id: I0d0a6eae1d62b16fbb822261c4536c4108a5866d
1 file changed