epoll: fix eventFd.add

eventFd.add hardcoded the value to add to 1 instead of using the
argument. This hasn't caused a bug since we never call add with
a different value.

Signed-off-by: Lorenz Bauer <lmb@isovalent.com>

internal/epoll/poller.go

@@ -211,7 +211,7 @@ func (efd *eventFd) close() error {
 
 func (efd *eventFd) add(n uint64) error {
 	var buf [8]byte
-	internal.NativeEndian.PutUint64(buf[:], 1)
+	internal.NativeEndian.PutUint64(buf[:], n)
 	_, err := efd.file.Write(buf[:])
 	return err
 }