TCP profile: avoid calling rohc_ntoh32() too many times in the same function
TCP profile: avoid calling rohc_ntoh32() too many times in the same function

It makes code clearer, and saves some lines.

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