This function is used to load additional, e.g. vendor specific, MIBs so that human readable OIDs like VENDOR-MIB::foo.1 instead of error prone numeric OIDs can be used.
The order in which the MIBs are loaded does matter as the underlying Net-SNMP library will print warnings if referenced objects cannot be resolved.
The filename of the MIB.
Returns true on success or false on failure.