User:Electron9/LLDP PoE

The setup phases are as follows:
 * PSE (provider) tests PD (consumer) physically using 802.3af phase class 3.
 * PSE powers up PD.
 * PD sends to PSE: I'm a PD, max power = X, max power requested = X.
 * PSE sends to PD: I'm a PSE, max power allowed = X.
 * PD may now use the amount of power as specified by the PSE.

The rules for this power negotiation are:
 * PD shall never request more power than physical 802.3af class
 * PD shall never draw more than max power advertised by PSE
 * PSE may deny any PD drawing more power than max allowed by PSE
 * PSE shall not reduce power allocated to PD, that is in use
 * PSE may request reduced power, via conservation mode