MBIM: fix compilation with GLib versions < 2.22.0

Change-Id: I27e794347dc0988f0f34798cb62f08a11a217176
Reviewed-on: https://code.wireshark.org/review/1400
Reviewed-by: Pascal Quantin <pascal.quantin@gmail.com>

epan/dissectors/packet-mbim.c

@@ -44,6 +44,14 @@
 #include "packet-usb.h"
 #include "packet-mbim.h"
 
+#if !GLIB_CHECK_VERSION(2,22,0)
+gboolean
+g_int64_equal(gconstpointer v1, gconstpointer v2)
+{
+  return *((const gint64*) v1) == *((const gint64*) v2);
+}
+#endif
+
 void proto_register_mbim(void);
 void proto_reg_handoff_mbim(void);