Fix OIDs for bypass group in ietf-mib.c

Reference http://tools.ietf.org/html/rfc1628#page-12
For bypass voltage, current and power
Fix OID for input.bypass.voltage in ietf-mib.c

Ooops, forgot fix one
Merge pull request #21 from AlexLov/patch-1

Fix OIDs for bypass group in ietf-mib.c