Fix the inner type of EpollFlags

Author: Mathias Svensson

src/sys/epoll.rs

@@ -7,7 +7,7 @@ use ::Error;
 
 bitflags!(
     #[repr(C)]
-    pub flags EpollFlags: u32 {
+    pub flags EpollFlags: libc::c_int {
         const EPOLLIN = libc::EPOLLIN as u32,
         const EPOLLPRI = libc::EPOLLPRI as u32,
         const EPOLLOUT = libc::EPOLLOUT as u32,