datapath: Suppress sparse complaints about address spaces.

datapath: Suppress sparse complaints about address spaces.

The sparse checker was complaining about incorrect address spaces (e.g.
__user versus non-__user pointers).  I looked at each of them, checked
that the code looked correct to me, and added the appropriate __force
annotations to casts.

Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: Jesse Gross <jesse@nicira.com>