[c-nsp] IOS-XR on 12K - 3.9.1 and SNMP

[Jared Mauch]

I strongly recommend against using this IOS-XR version if you require SNMP in your environment.

I've found a variety of "really bad" bugs.

When polling via snmpv1 the 64-bit counters may not respond (at all)

when polling via snmpv2 some counters (eg: ifOutDiscards) are missing.

- Jared