Added little fix in get_interfaces in snmp.AirOS
Iprovements to firmware method in smnp.AirOS backend related to #5 and #19
Iprovements to manufacturer method in smnp.AirOS backend related to #5 and #19
Iprovements to model method in smnp.AirOS backend related to #5 and #19
Added get_signal_strength method in smnp.AirOS backend + test
Related to #5 and #19
Change from manufactuer to get_manufacturer in snmp.AirOS backend
Related to #5 and #19
Improvements to snmp.AirOS backend related to #5 and #19
 * get_interfaces_mtu + test method
 * change from get_manufacturer to manufacturer