Set POLLRDHUP on Linux when polling rtpproxy's socket to drain

any unclaimed data. This seems to be necessary on TCP sockets
otherwise poll() appears to hang indefinitely if rtpproxy has been
terminated despite timeout being set to 0 (i.e. don't block).

With this flag set the disconnect is properly detected and socket
is re-connected after configured timeout.

modules/rtpproxy/rtpproxy.c

@@ -139,6 +139,8 @@
  *            (osas)
  */
 
+#define _GNU_SOURCE
+
 #include <sys/types.h>
 #include <netinet/in.h>
 #ifndef __USE_BSD
@@ -325,6 +327,9 @@ int update_rtpp_proxies();
 
 static inline void raise_rtpproxy_event(struct rtpp_node *node, int status);
 
+#if !defined(POLLRDHUP)
+#define POLLRDHUP 0
+#endif
 
 static struct {
 	const char *s;
@@ -2128,12 +2133,12 @@ send_rtpp_command(struct rtpp_node *node, struct iovec *v, int vcnt)
 		}
 	} else {
 		fds[0].fd = rtpp_socks[node->idx];
-		fds[0].events = POLLIN;
+		fds[0].events = POLLIN | POLLRDHUP;
 		fds[0].revents = 0;
 		/* Drain input buffer */
 		while ((poll(fds, 1, 0) == 1) &&
 		    ((fds[0].revents & POLLIN) != 0)) {
-			if (fds[0].revents & (POLLERR|POLLNVAL)) {
+			if (fds[0].revents & (POLLERR|POLLNVAL|POLLRDHUP)) {
 				LM_ERR("error on rtpproxy socket %d!\n", rtpp_socks[node->idx]);
 				break;
 			}