plymouth: fix ply proto endianess issues

Plymouth enforces LE even for the local Ply proto, hence we should do
the conversion properly for BE arch compat.

Tracked down by Harald Hoyer.

https://bugzilla.redhat.com/show_bug.cgi?id=744415

src/tty-ask-password-agent.c

@@ -206,6 +206,7 @@ static int ask_password_plymouth(
                                 continue;
 
                         memcpy(&size, buffer+1, sizeof(size));
+                        size = le32toh(size);
                         if (size+5 > sizeof(buffer)) {
                                 r = -EIO;
                                 goto finish;