[OPTIM] ev_sepoll: detect newly created FDs and check them once

[OPTIM] ev_sepoll: detect newly created FDs and check them once

When an accept() creates a new FD, it is already marked as set for
reads. But the task will be woken up without first checking if the
socket could be read.

The speculative I/O gives us a chance to either read the FD if there
are data pending on it, or immediately mark it for poll mode if
nothing is pending.

Simply doing this reduces the number of calls to process_session
from 6 to 5 per session, 2 to 1 calls to process_request, 10% less
calls to epoll_ctl, fd_clr, fd_set, stream_sock_data_update, 20%
less eb32_insert/eb_delete, etc... General performance increase
seems to be around 3%.