This patch is specifically for the WWM/wind project. It unconditionally
sets the soft limit of open file descriptors to the hard limit. It is
'unconditionally' in two meanings:

1. Always set it and don't depend on instance configuration (via
   'instance.json). We certainly want this in the WWM/wind instance and
   adding the option to SlapOS would lead to a lot of copy-pasted SlapOS
   instance files in the WWM project, which are noisy, difficult to
   maintain and tedious to create.

2. Always set it and don't depend on the used server (Medusa or WSGI).
   In the upstream patches nexedi/erp5@39369169
   and nexedi/erp5@c42c1d38
   the option is only made available when using WSGI. But in our production
   instance we may want to switch back to ZServer/Medusa, which is why
   we need an ERP5 which supports the option independent from the used
   server.