Mark Howerton

Added support for Counter64 in asn1 and ber (for snmp v2c)

1

**Checklist:** - [ x] If you are new to Scapy: I have checked [CONTRIBUTING.md](https://github.com/secdev/scapy/blob/master/CONTRIBUTING.md) (esp. section submitting-pull-requests) - [ x] I squashed commits belonging together - [ x] I added...

### Brief description It looks like Counter64 value type was added years ago but at some point was taken out. It was previously in https://github.com/secdev/scapy/commit/2e776b7917d60e640d15e4d4fb3015217443b233 ### Scapy version 2.5 ###...