encoding: Redesign Encoding::write_immediate_assignment API

The EGPRS support will need more information to encode the IMMEDIATE
ASSIGMENT. Instead of adding more parameters pass a pointer to the
TBF unless an SBA shall be done (indicated by tbf == NULL). All
values that can be derived from the TBF and are not needed for an SBA
are removed from the parameter list.

Return a negative value on error.

Sponsored-by: On-Waves ehf
4 files changed