keventd: use poll.h, not sys/poll.h, fix warning on musl libc
#include <errno.h>
#include <dirent.h>
+#include <poll.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <syslog.h>
#include <unistd.h>
-#include <sys/poll.h>
#include <sys/socket.h>
#include <sys/types.h>
