nge: fix no previous prototype for ‘proto_register_nge/handoff_nge’ [-Wmissing-prototypes]

Change-Id: I2e7cecad96390f709c6a135b6059c01712971dfe
Reviewed-on: https://code.wireshark.org/review/21571
Reviewed-by: Charlie Lenahan <clenahan@sonicbison.com>
Reviewed-by: Michael Mann <mmann78@netscape.net>

epan/dissectors/packet-netgear.c

@@ -26,6 +26,9 @@
 
 #include <epan/packet.h>
 
+void proto_register_nge(void);
+void proto_reg_handoff_nge(void);
+
 #define NETGEAR_ENSEMBLE_PORT 4554
 
 static int proto_nge = -1;