The gw_time defines the RX time by the gateway, the ns_time defines when
it was received by the NS. The latter could for example help to debug
latency between the GW <> NS.
Historically, the tx power was defined as ERP. The Semtech UDP Packet
Forwarder protocol was never explicit if the "powe" field was in ERP or
EIRP. However, as the antenna gain in the Semtech UDP Packet Forwarder
is documented as dBi and is deducted from the "powe" field, this means
that "powe" is in EIRP.
This commit corrects all values to EIRP, to make sure that if the
antenna gain is properly configured (which should be), that the correct
rf_power is used by the gateway.
This includes:
* Changing the modulation parameters to its own type.
* Changing the timing parameters to its own type.
* Change the gateway_id to string. As the json encoding for bytes fields
is base64, this was confusing some users.
* Change the uplink / downlink id to uint32 from uuid. A string
representation of the UUID field (for the same reason as the gateway
id) would consome quite some additional bytes. An uint32 provides
sufficient uniqueness for the purpose of uplink / downlink.
