#9 Add new epoll methods "modify_*sock"

[Joachim Bauch]

It would be great to have epoll methods to modify the events that should be listened for.

Currently you have to call "epoll_remove_usock" and "epoll_add_usock" to switch from UDT_EPOLL_IN | UDT_EPOLL_OUT to UDT_EPOLL_IN only. Same for the system sockets where you could use EPOLL_CTL_MOD internally.