drivers/apc-mib.c: update MIB values

[moenoel]

Some of the mapped SNMP values for the APC MIB are incomplete/out of date, most importantly for the OID ".1.3.6.1.4.1.318.1.1.1.4.1.1.0" (upsBasicOutputStatus). This causes NUT to report that it lost connection to a UPS that is e.g. in the "ECOnversion" operation mode, as the corresponding unmapped value results in an empty ups.status.

I updated this and a few other things based on PowerNet MIB v4.5.2 and the SNMP documentation for APC Galaxy VS/PX/VL UPSes.

Some things that probably need to be looked at before this can be merged:

• I am unsure whether there is a better thing to return than "LB" for the batteryInFaultCondition(4) and noBatteryPresent(5) states. I put "LB" for now as a fail safe way to handle them.
• I was unable to find documentation for the states powerSavingMode(18), activeLoad(23), chargerOnly(26) and distributedEnergyReserve(27), so I left them empty for now. Seems like they're not inuse for the UPS I'm interested in here, at least.
• I added a keyword ECO to the return values for ecoMode(13) and eConversion(20). Not sure if that might break anything or be of value to anyone for monitoring purposes and whatnot.

[jimklimov]

Just in case, seems related to #2239 which tackled at least some more OIDs (but in a less efficient fashion, making a separate subdriver).