Certain ICMP error replies cause ping to perform a reverse DNS

lookup on an IP address from the packet (such as the IP that sent
a TTL exceeded error). If the DNS lookup takes a long time, ^C will
appear to be ineffective since the SIGINT handler just sets a flag
and returns. Work around this by exiting immediately on receipt of
a second SIGINT when DNS lookups are enabled.

PR:		bin/4696
MFC after:	1 week

sbin/ping/ping.c

@@ -830,6 +830,12 @@ stopit(sig)
 	int sig __unused;
 {
 
+	/*
+	 * When doing reverse DNS lookups, the finish_up flag might not
+	 * be noticed for a while.  Just exit if we get a second SIGINT.
+	 */
+	if (!(options & F_NUMERIC) && finish_up)
+		_exit(nreceived ? 0 : 2);
 	finish_up = 1;
 }