GTK Remote Capturing

Move the GTK files necessary for managing the recnet remote host from capture_dlg.c to recent.c in order to use them in QT, too.

Change-Id: I3f3fd31ce928162de08c6db7309ef2a9b1e97760
Reviewed-on: https://code.wireshark.org/review/2955
Reviewed-by: Anders Broman <a.broman58@gmail.com>