nmea out in MP not work in Reefmaster for live mapping

#### Issue details
Nmea out in MP is not work in Reefmaster for live mapping (depth mapping soft). Meanwhile DrDepth (another depth mapping software) works only if ignore nmea sum is checked. Perhaps the “Ingore NMEA checksum” is a clue - perhaps MP’s NMEA output isn’t providing a correct checksum.

#### Version
All

#### Platform
[ x ] All

#### Airframe type
All

#### Hardware type
All

#### Logs
no logs

Start by reproducing Mission Planner's NMEA output with Reefmaster live mapping and with DrDepth, checking whether the output checksum is valid and whether ignoring checksums changes the result. Done means NMEA output from Mission Planner works in Reefmaster without requiring an “Ignore NMEA checksum” option; no source file or test is identified in the issue.

Written by the indexing model from the issue text.