#7 Add extra gain/loss information to interfaces

[Ian Lister]

Currently the database records antenna gain (in dBi) for each
interface. It would be useful if it also recorded radio output power
(in mW or dBm) and any cable/connector loss (in dB).

This would allow calculation of EIRP, and would enable appropriate
warnings for interfaces recorded as being over the maximum legal
limit.

Ian