[FEATURE]: configurable option SUBNET in module PERMISSIONS

[fluke87]

There is a subnet delimiter in the PERMISSIONS module
https://github.com/OpenSIPS/opensips/blob/3.0/modules/permissions/hash.h#L105
in a production environment, this setting needs to be changed depending on your installation.
however, changing this parameter through the source code is not always optimal and not beneficial.
In this connection, it is proposed to introduce the possibility of setting this parameter through the module configuration.

[liviuchircu]

Hello! The removal of the "128" subnets limitation has been implemented in #3560 and is to be merged soon. Together with some big performance improvements on the subnet lookup algorithm which may start to become noticeable if you typically load up large volumes of addresses into your OpenSIPS.