OPTIM: splice: detect shutdowns and avoid splice() == 0

Since last commit introducing EPOLLRDHUP, the splicing code is able to
detect an incoming shutdown without calling splice() == 0. This avoids
one useless syscall.
diff --git a/src/raw_sock.c b/src/raw_sock.c
index 20a867a..9528911 100644
--- a/src/raw_sock.c
+++ b/src/raw_sock.c
@@ -148,6 +148,10 @@
 		retval += ret;
 		pipe->data += ret;
 
+		/* if a POLL_HUP was present, we've read the last segment */
+		if ((fdtab[conn->t.sock.fd].ev & (FD_POLL_ERR|FD_POLL_HUP)) == FD_POLL_HUP)
+			goto out_read0;
+
 		if (pipe->data >= SPLICE_FULL_HINT || ret >= global.tune.recv_enough) {
 			/* We've read enough of it for this time, let's stop before
 			 * being asked to poll.