Do not broadcast empty messages

[BluemarkInnovations]

The BT5. WLAN NaN and WLAN broadcast function use the odid_message_build_pack function of the opendrone ID lib to encode data. That function uses the "valid" vars of each packet (basicID, location, system etc) to determine if it needs to be encoded. The BT4 transmission uses a slightly different approach, not using these "valid" vars

In this PR:

• use the "valid" vars for BT4 transmission too (to have similar behavior for all transmission protocols)
• only set SelfID and operatorID packets to valid if data is entered.

[BluemarkInnovations]

I've dropped the valid zeroing change, better to have #104

Agree.