Fix to solo/monin_obukhov_drag.F90

[bensonr]

Describe the bug
There is a namespace collision with monin_obukhov.F90 from FMS and solo/monin_obhukov_drag.F90 in FV3. These F90 modules both have the same name, which can lead to collisions when both include directories are present.

To Reproduce
N/A

Expected behavior
Each file should have a unique module name.

System Environment
Describe the system environment, include:
N/A

Additional context
N/A