epoll: fix EPOLLET checking condition

Because bitwise "&" was used instead of logical "&&" the condition
was always false:

  (e & EPOLLET) & !warned = 0x80000000 & 1 = 0

And the warning "EPOLLET ignored" was never printed.

Reviewed-by: Nadav Har'El <nyh@cloudius-systems.com>
Signed-off-by: Tomasz Grabiec <tgrabiec@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>