feature: add possibility to modify the DrvEdd sendpriority when LLDP sends a frame

for usage with different switch implementations it is required to have influence (at compile time) to how the LLDP task uses the DrvEdd interface to send its own frames.

new switch implementations support handling of network control frames, older switches do not.

To mark LLDP frames as network control frame it is required to use a special syntax of DrvEdd that shall not be used if the underlying switch does not support this network control handling