SWITCH_TYPE is not always defined, SwitchType() will try to find a fallback

Pick up change from Samba:

    commit 4b09df897803e78265fd19f6ff19be6e3d8a3944
    Author: Matthieu Patou <mat@matws.net>
    Date:   Tue Oct 1 12:10:18 2013 -0700

    pidl-wireshark: SWITCH_TYPE is not always defined, SwitchType() will try to find a fallback

    Pair-Programmed-With: Stefan Metzmacher <metze@samba.org>

Change-Id: I1f41ece23e8fec30f9cd89a2203ad63ee6e21e36
Reviewed-on: https://code.wireshark.org/review/5105
Reviewed-by: Guy Harris <guy@alum.mit.edu>