cleanup: merge rohc_comp_find_context_from_packet() and c_find_context()
cleanup: merge rohc_comp_find_context_from_packet() and c_find_context()

Merge the rohc_comp_find_context_from_packet() and c_find_context() functions
into a single rohc_comp_find_ctxt() function. This avoid having 2 functions
with similar names doing 2 different parts of the same job.

didier-barvaux/rohc,didier-barvaux/rohc,didier-barvaux/rohc,didier-barvaux/rohc,didier-barvaux/rohc