core: io wait - unhash in case delete operation fails because of EBADF

- EBADF: epfd or fd is not a valid file descriptor

(cherry picked from commit 846cc5b)

src/core/io_wait.h

@@ -669,6 +669,13 @@ inline static int io_watch_del(io_wait_h* h, int fd, int idx, int flags)
 					if (errno==EAGAIN) goto again_epoll;
 					LM_ERR("removing fd %d from epoll list failed: %s [%d]\n",
 						fd, strerror(errno), errno);
+					if (unlikely(errno==EBADF)) {
+						LM_ERR("unhashing of invalid fd - %d (epfd %d)\n", fd,
+								h->epfd);
+						unhash_fd_map(e);
+						h->fd_no--;
+					}
+
 					goto error;
 				}
 #ifdef EPOLL_NO_CLOSE_BUG