Feature: snmp get bulk support configuration

[g-bougard]

Permits to set values in etc/snmp-advanced-support.cfg:

1. To force maxrepetitions to 0 to leave Net::SNMP the choice to use get-bulk-request with the best value. The usual value is 25.
2. To force maxrepetitions to be set to any positive value.
3. When default of 1 is kept, for each device: glpi-agent will try to run a request with maxrepetitions set to 2 as minimum, then
   1. If the try returns more than one value, we will continue to use get-bulk-request setting max-repetitions to 0 for the device,
   2. Otherwise, maxrepetitions is kept as 1 for the device.
4. To disable bulk support discovery on devices, skip-bulk-support-discovery can be set to 1. It defaults to 0.
5. The discovery is done on mib-2.system oid which should be supported by most devices. Another oid can be set by setting bulk-support-discovery-oid. It defaults to .1.3.6.1.2.1.1.