vcl: fix nonblocking accept with >1 event in the queue

We discard unwanted events until we get an ACCEPTED.
But if we are non-blocking we need to check the queue
length every time and EAGAIN if empty before waiting.

Type: fix

Signed-off-by: Carl Smith <carl.smith@alliedtelesis.co.nz>
Change-Id: Ie0c7e5cb00f0d37d2e1534f8bb384221ff56f2e3