BUG/MINOR: startup: certain goto paths in init_pollers fail to free

BUG/MINOR: startup: certain goto paths in init_pollers fail to free

If we fail to initialize pollers due to fdtab/fdinfo/polled_mask
not getting allocated, we free any of those that were allocated
and exit. However the ordering was incorrect, and there was an old
unused and unreachable "fail_cache" path as well, which needs to
be taken when no poller works.

This was introduced with this commit during 1.9-dev :
   cb92f5c ("MINOR: pollers: move polled_mask outside of struct fdtab.")

It needs to be backported to 1.9 only.