Don't parse services file twice, respect user settings

Don't parse services file twice, respect user settings

Platform file '/etc/services' is the same as Wireshark's
'/usr/share/wireshark/services', only Wireshark's is more recent
(on my system, same goes for other platforms I assume).

Use only Wireshark's IANA services files.

Other benefits would be removing some platform specific #ifdefs and making
service names more consistent.

Also respect user services settings by parsing $PERSCONFIG_DIR/services
after $SYSCONFIG_DIR/services.

Change-Id: I9890473af92763e02dabd2386eaa767aed2f2899
Reviewed-on: https://code.wireshark.org/review/10941
Petri-Dish: Michael Mann <mmann78@netscape.net>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Michael Mann <mmann78@netscape.net>