Properly implement the "id" callback argument in the "idr_for_each" function
in the LinuxKPI. The old implementation assumed only one IDR layer was present.
Take additional IDR layers into account when computing the "id" value.

MFC after: 1 week
Found by: Karthik Palanichamy <karthikp@chelsio.com>
Tested by: Karthik Palanichamy <karthikp@chelsio.com>
Sponsored by: Mellanox Technologies