Minor SNMP MIB Improvements

1) WHISP-APS-MIB: There is no SNMP OID for showing if a session is operating on primary, secondary, or tertiary on the AP's MIB. This information can be found on the SM MIB (WHISP-SM-MIB), but it would be very useful to have this session information available from the AP as well.

2) WHISP-SM-MIB: . (radioTxPwr) on PMP450 SM returns OCTET STRING, IE "22 dBm". A radioTxPwrInt OID is needed to return an integer, IE "22".