Added support for additional Moxa EDS-G models

[rhinoau]

Support for additional Moxa EDS-G units G512E and G516E

From the limited test data on the existing models it's hard to confirm others but it looks like IKS and EDSP serialNumber lines were breaking some discovery items for all models with exit 1 - removed. Both MIBs do not include such an entry.

Discovery debug output:

Exitcode: 1  

MOXA-IKS6726A-MIB::serialNumber: Unknown Object Identifier
MOXA-EDSP510A8POE-MIB::serialNumber: Unknown Object Identifier  

DO NOT DELETE THE UNDERLYING TEXT

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[PipoCanaja]

LGTM