alproto: improve AppProtoToString

Make AppProtoToString compilation fail on missing 'case's.

src/app-layer-protos.c

@@ -30,8 +30,9 @@
 const char *AppProtoToString(AppProto alproto)
 {
     const char *proto_name = NULL;
+    enum AppProtoEnum proto = alproto;
 
-    switch (alproto) {
+    switch (proto) {
         case ALPROTO_HTTP:
             proto_name = "http";
             break;

src/app-layer-protos.h

@@ -25,7 +25,7 @@
 #ifndef __APP_LAYER_PROTOS_H__
 #define __APP_LAYER_PROTOS_H__
 
-enum {
+enum AppProtoEnum {
     ALPROTO_UNKNOWN = 0,
     ALPROTO_HTTP,
     ALPROTO_FTP,
@@ -53,6 +53,7 @@ enum {
     ALPROTO_MAX,
 };
 
+/* not using the enum as that is a unsigned int, so 4 bytes */
 typedef uint16_t AppProto;
 
 /**