iwlwifi: mvm: add description to a few generic assert numbers

iwlwifi: mvm: add description to a few generic assert numbers

FW asserts 0x70, 0x71, and 0x73 all just mean that the real error
happened in another MAC, and to look there for the problem. Add their
descriptions to the assert number lookup table so users get a nicer
error message in the logs.
Also, since the 4 most-significant bits of the assert number are
dynamic, and depend on which MAC the assert occurred on, ignore those
bits when looking up the assert name.

Signed-off-by: Naftali Goldstein <naftali.goldstein@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>