Description: The interface group ID, the same as hh3cMDCGroupIdentity.
There are two parts for this id.

depicted as follows:
31                  7                  0
+++++++++++++++++++++++++++++++++++++++++
+   entity index    +    group index    +
+   ( bit 8..31 )       ( bit 0..7 )    +
+++++++++++++++++++++++++++++++++++++++++

From bit0 to bit7 (one byte), it is interfaces group index.

From bit8 to bit31 (three bytes), it is the physical index
the same as the entPhysicalIndex specified in ENTITY-MIB.
Note that only entPhysicalIndex values that represent
physical boards (i.e., associated entPhysicalClass value is
'module(9)') are permitted to exist in this table.