New object: rtr-set
defines a set of routers specified by inet-rtr names, ipv4_addresses or other rtr-set names
rtr-set: [mandatory] [single] [primary/look-up key]
descr: [mandatory] [multiple]
members: [optional] [multiple]
mbrs-by-ref: [optional] [multiple]
remarks: [optional] [multiple]
tech-c: [mandatory] [multiple] [inverse key]
admin-c: [mandatory] [multiple] [inverse key]
notify: [optional] [multiple] [inverse key]
mnt-by: [mandatory] [multiple] [inverse key]
changed: [mandatory] [multiple]
source: [mandatory] [single]