change pfIfDescr and pfLogIfName from plain OCTET STRING (which has no

change pfIfDescr and pfLogIfName from plain OCTET STRING (which has no
textual-convention so is sometimes printed as hex dump) to DisplayString
(ascii).

likewise change pfLabelName and pfTblName to SnmpAdminString (UTF-8
textual-convention).

feedback/tweaks (notably pointing out UTF-8)/ok martijn@