Fix missing A in getopt.

From Michael Grant.

babeld.c

@@ -127,7 +127,7 @@ main(int argc, char **argv)
     protocol_port = 8475;
 
     while(1) {
-        opt = getopt(argc, argv, "m:p:h:H:i:k:PsS:d:g:lwt:T:c:C:DL:I:");
+        opt = getopt(argc, argv, "m:p:h:H:i:k:A:PsS:d:g:lwt:T:c:C:DL:I:");
         if(opt < 0)
             break;