list compression: fix wrong bit shifts
list compression: fix wrong bit shifts

Coverity Scan reported that some bit shifts in the list compression of
the RFC3095 profiles were wrong. Only the 4-bit XI fields were impacted.

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