lorawan doesnt support setting the FPort #846
Description
A default FPort of 1 is used now.
The use of FPort (similar to port aka service in TCP) is quite widespread and can, formally, reduce the payload with 1 single byte.
The lorawan implementation should not hide the FPort from the API.
I'm happy to submit a pull-request where the Session struct has a extra field: FPort and the code where fport is set to 1 now consults the presence of a legal FPort in the Session struct first.