fix SNMPv3 version identifier
no need to pass manufacturer anymore

We try to switch SNMP context for any device failing to provide any
result for dot1qTpFdbPort.
exclude VLAN 1, it is the default context
initial import

This module bring supports for modern MegaRAID controllers.

see: #2361
availability of megacli command is enough

see: #2361
cosmetic cleanups

see: #2361
simplification: use getFirstMatch()

see: #2361