tests: don't hardcode length values of expected encoding gsm_7bit_encode:

make sure to return the number of actually written bytes gsm_7bit_decode:
calculate length of resulting septets from input length before decoding

The input length to gsm_7bit_decode reflects the number of encoded bytes
to be decoded. As the decoding is done on the input in septetes we need
to take this into account and recalculate the length.
2 files changed