MXS-2574: Add PATCH for /users/inet endpoint

The alteration of user passwords is now done inside MaxScale. This
prevents the possibility of a user locking themselves out.

include/maxscale/adminusers.h.in

@@ -71,6 +71,7 @@ const char* admin_disable_linux_account(const char *uname);
 bool admin_linux_account_enabled(const char *uname);
 
 const char* admin_add_inet_user(const char *uname, const char *password, enum user_account_type type);
+const char* admin_alter_inet_user(const char* uname, const char* password);
 const char* admin_remove_inet_user(const char* uname);
 bool admin_inet_user_exists(const char *uname);
 bool admin_verify_inet_user(const char *uname, const char *password);