Fix signal handler from getting stuck in an endless loop

The signal handler for SIGINT/TERM/QUIT and, importantly, SIGPIPE tries
to write an informational message to stderr. When however stderr is
redirected to a closed pipe, this will cause (another) SIGPIPE, and in
turn the signal handler will get called again, and again and again.

Since we intend to exit rtl_fm anyways, we can just ignore this signal.

src/rtl_tcp.c

@@ -144,6 +144,7 @@ sighandler(int signum)
 #else
 static void sighandler(int signum)
 {
+	signal(SIGPIPE, SIG_IGN);
 	fprintf(stderr, "Signal caught, exiting!\n");
 	rtlsdr_cancel_async(dev);
 	do_exit = 1;