CaptureDialog: Fix IF type for user created pipe

- If a user adds a pipe via "Capture Options"->"Manage Interfaces"
   ->"Pipes" the device.if_type.type is either not filled out (in
   the case if no other interfaces exist), or will be set to the
   last set if_type of the device queried by the iteration in line
   3537.

 - One could argue, that this is just a fixup, as still the issue
   remains, that the device structure will not be resetted, after
   the search for an already existing pipe element. Maybe a separate
   variable should be used for searching as it is used for adding
   the pipe

Change-Id: Ia727bf3ce270a62d065e8c524a13768af389c346
Reviewed-on: https://code.wireshark.org/review/1296
Reviewed-by: Alexis La Goutte <alexis.lagoutte@gmail.com>

ui/gtk/capture_dlg.c

@@ -3485,6 +3485,7 @@ add_pipe_cb(gpointer w _U_)
     device.if_info.vendor_description = NULL;
     device.if_info.addrs = NULL;
     device.if_info.loopback = FALSE;
+    device.if_info.type = IF_PIPE;
 #if defined(HAVE_PCAP_CREATE)
     device.monitor_mode_enabled   = FALSE;
     device.monitor_mode_supported = FALSE;