avformat/httpauth: Change enum to int, which is accessed via AVOption as int

This fixes depending on implementation defined behavior
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/httpauth.h

@@ -56,7 +56,7 @@ typedef struct HTTPAuthState {
     /**
      * The currently chosen auth type.
      */
-    HTTPAuthType auth_type;
+    int auth_type;
     /**
      * Authentication realm
      */