Improve SMPP processor interface docstrings.
Improve SMPP processor interface docstrings.

harrissoerja/vumi,TouK/vumi,vishwaprakashmishra/xmatrix,harrissoerja/vumi,vishwaprakashmishra/xmatrix,TouK/vumi,harrissoerja/vumi,vishwaprakashmishra/xmatrix,TouK/vumi