Fix compilation when compiling without libpcap (configure script parameter

Fix compilation when compiling without libpcap (configure script parameter
"--without-pcap")

Note: Generates run-time warnings still:

(wireshark:66065): Gtk-WARNING **: CaptureFilters: missing action /Capture/CaptureFilters

(wireshark:66065): Gtk-WARNING **: Interfaces: missing action /Capture/Interfaces

(wireshark:66065): Gtk-WARNING **: Options: missing action /Capture/Options

(wireshark:66065): Gtk-WARNING **: Start: missing action /Capture/Start

(wireshark:66065): Gtk-WARNING **: Stop: missing action /Capture/Stop

(wireshark:66065): Gtk-WARNING **: Restart: missing action /Capture/Restart

git-svn-id: http://anonsvn.wireshark.org/wireshark/trunk@38782 f5534014-38df-0310-8fa8-9805f1628bb7