ofproto-dpif-rid: remove struct rid_map

struct rid_map only has one member which is a struct hmap.
This allows for a slight simplification of the code by removing
struct rid_map and using a struct hmap directly instead.

Signed-off-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: Andy Zhou <azhou@nicira.com>
ofproto-dpif-rid: remove unused return value of rid_pool_add()

The return value of rid_pool_add() is never used
so the code may be slightly simplified by removing it.

Signed-off-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: Andy Zhou <azhou@nicira.com>