evport: Remove artificial low limit on max events per getn call

evport: Remove artificial low limit on max events per getn call

Previously, evport could only handle up to 8 events per time through
the loop.  This would impose an artificially high number of syscalls
on us to retrieve a large number of events.

This code allows the EVLOOP_* flags to work more similarly to how
they do on other platforms (up to 4096 events per syscall).  Dispite
dire warning (from 2006), doing this won't impose a big incremental
RAM penalty: if you have 4096 events firing at once, you necessarily
have a proportional number of events pending, and their associated
data structures are already costing a good bit of RAM.

This patch makes the main/many_events_slow_add test pass again.