Fix Extreme XOS Vlan stuff

Would be nice if Observium could discover the VLAN's for Extreme XOS switches - it discovers tham but adds them as interfaces rather than as VLAN's.

I suspect this is probably because Extreme are dicks and seem to really suck at SNMP - but apparently there is a MIB which gives the definitions for the VLAN table on XOS. (EXTREME-VLAN-MIB)

1.3.6.1.4.1.1916.1.2 is the Extreme vlan mib,
1.3.6.1.4.1.1916.1.2.1.2.1.10 is the vlanid
1.3.6.1.4.1.1916.1.2.1.2.1.2 is the vlan description

I can help out debugging if needs be - I just cant write code to save myself