android: Explicitly apply DNS servers to the TUN device

android: Explicitly apply DNS servers to the TUN device

If the peer deletes the CHILD_SA, we recreate it due to the close
action.  However, if we create a new TUN device, we do so with a new
VpnService.Builder object and on that the DNS servers were never applied.
The latter happened only on the fly in the attribute handler when an
IKE_SA was established.  Now we do this explicitly when creating the TUN
device, like the virtual IPs and routes.  While we could avoid the
recreation of the TUN device if the CHILD_SA is recreated, there is the
theoretical possibility that the remote traffic selectors change.  This
way we also avoid adding stuff to the builder in different places.

Fixes #3637.