First, a "bug fix": By coincidence the snmpit Cisco module was able to
build up the mod/port-to-ifindex mapping on newer switches where
interface descriptions include a submodule ID (e.g.
"GigabitEthernet1/0/1" vs. "GigabitEthernet1/1"). However, it was
actually just grabbing the submodule ID in place of the module ID.  This
is OK (in some loose sense) for non-modular switches where everything is
effectivley on the same module. Not good for IOS/NX-OS switches with
actual modules and submodule identifiers. Things would not have worked
for these.  As a fix that retains backward compatibility, the Cisco
snmpit module now correctly extracts the module ID, but subtracts '1'
from it.  This allows existing installations that have zero-based module
numbering in their database for non-modular IOS/NX-OS switches with
submodule IDs to continue to work as is.

The above nonsense is not what I set out to do, however, and the commit
just gets worse. I extended the hack for non-modular switches with a mix
of gigabit and ten gigabit to bump any ten gigabit interface port's
module ID to "1". The existing hack already did this for non-modular
switches with a mix of fast Ethernet and gigabit.  Absolutely horrific.
I need a shower.