CA-101788: increase xenconsoled default number of fds in xenservices from 1024 to 4096

xenconsoled is currently started in xenservices using the default ulimit -n
value 1024. This aligns well with the limit of 1024 fds that the xenconsoled
select() can handle. Each vm console will tipically use 3 fds (4 if logging
is enabled), limiting the number of consoles in dom0 to a couple of hundred.

The new upstream xenconsoled uses poll() instead of select() and can handle
>1024 fds, as long as its ulimit -n value is properly set up in xenservices.
Increasing this value to 4096 will allow us to have 1000 vm consoles in dom0,
which is more aligned to other values.

Signed-off-by: Marcus Granado <marcus.granado@citrix.com>