Let snmpd check a response package against the requested searchrange end.

Let snmpd check a response package against the requested searchrange end.

If the returned OID is beyond the searchrange end we have two cases:
- If the backend supports searchranges (agentx) we generate a GENERR and
  close the connection.
- If the backend doesn't support searchranges (legacy and maybe a future
  snmp proxy) we simply fix-up the result.

OK tb@