eal/linux: fix epoll timeout

Function rte_epoll_wait should return when underlying call
to epoll_wait times out.

Signed-off-by: Robert Sanford <rsanford@akamai.com>
Acked-by: Cunming Liang <cunming.liang@intel.com>

lib/librte_eal/linuxapp/eal/eal_interrupts.c

@@ -1002,6 +1002,9 @@ rte_epoll_wait(int epfd, struct rte_epoll_event *events,
 				strerror(errno));
 			rc = -1;
 			break;
+		} else {
+			/* rc == 0, epoll_wait timed out */
+			break;
 		}
 	}