This object indicates the AAL5 data encapsulation
detected by PPPoA (PPP over ATM) or PPPoEoA (PPP over
Ethernet over ATM).
The value is only applicable if sapAtmEncapsulation is
set to 'auto' and returns 'unknown' as long as no
encapsulation is detected.
If sapAtmEncapsulation is set to a value different than
'auto', sapAtmDetectedEncapsulation always returns the
same value as sapAtmEncapsulation.