gril: Change parcel code to check parcel sanity

We check if the parcel contains enough data and with the right format
when we read a field.
rilmodem: Right initialization for parcel
src: Return latest error in sim-mnclength driver
unit: Add tests for mnclength plugin
build: Add tests for mnclength plugin
Merge pull request #38 from alfonsosanchezbeato/mnclength-test

mnclength test
Merge pull request #37 from alfonsosanchezbeato/parcel-safe

Make parcel code safer