[snmp] customisable `oid_batch_size` batch size
[snmp] customisable `oid_batch_size` batch size

Make the OID batch size configurable. Create a 'hidden' `oid_batch_size`
option in the `init_config` section of the check YAML configuration
file (default to 10).
Helpful to troubleshoot and workaround batch query related cases.

manolama/dd-agent,huhongbo/dd-agent,gphat/dd-agent,jyogi/purvar-agent,brettlangdon/dd-agent,pmav99/praktoras,jyogi/purvar-agent,AntoCard/powerdns-recursor_check,Wattpad/dd-agent,cberry777/dd-agent,takus/dd-agent,c960657/dd-agent,AntoCard/powerdns-recursor_check,cberry777/dd-agent,manolama/dd-agent,indeedops/dd-agent,manolama/dd-agent,AntoCard/powerdns-recursor_check,gphat/dd-agent,manolama/dd-agent,huhongbo/dd-agent,tebriel/dd-agent,tebriel/dd-agent,mderomph-coolblue/dd-agent,c960657/dd-agent,manolama/dd-agent,urosgruber/dd-agent,mderomph-coolblue/dd-agent,takus/dd-agent,Mashape/dd-agent,takus/dd-agent,takus/dd-agent,jyogi/purvar-agent,indeedops/dd-agent,urosgruber/dd-agent,Mashape/dd-agent,pmav99/praktoras,amalakar/dd-agent,urosgruber/dd-agent,AntoCard/powerdns-recursor_check,lookout/dd-agent,c960657/dd-agent,Mashape/dd-agent,AntoCard/powerdns-recursor_check,lookout/dd-agent,pmav99/praktoras,mderomph-coolblue/dd-agent,amalakar/dd-agent,brettlangdon/dd-agent,pmav99/praktoras,gphat/dd-agent,lookout/dd-agent,huhongbo/dd-agent,Mashape/dd-agent,amalakar/dd-agent,Mashape/dd-agent,gphat/dd-agent,c960657/dd-agent,mderomph-coolblue/dd-agent,c960657/dd-agent,indeedops/dd-agent,lookout/dd-agent,brettlangdon/dd-agent,jyogi/purvar-agent,Wattpad/dd-agent,amalakar/dd-agent,cberry777/dd-agent,cberry777/dd-agent,cberry777/dd-agent,urosgruber/dd-agent,tebriel/dd-agent,Wattpad/dd-agent,huhongbo/dd-agent,pmav99/praktoras,brettlangdon/dd-agent,amalakar/dd-agent,Wattpad/dd-agent,brettlangdon/dd-agent,indeedops/dd-agent,tebriel/dd-agent,Wattpad/dd-agent,takus/dd-agent,huhongbo/dd-agent,indeedops/dd-agent,lookout/dd-agent,tebriel/dd-agent,jyogi/purvar-agent,mderomph-coolblue/dd-agent,gphat/dd-agent,urosgruber/dd-agent