datapath: Remove redundant nw_ prefix from fields in flow key.

datapath: Remove redundant nw_ prefix from fields in flow key.

The fields of the kernel flow key are now grouped by protocol rather
than using generic names.  The containing structures describe the
category, so it is no longer necessary to use prefixes.  Most of
these prefixes have been removed but nw_proto and nw_tos have
retained them.  This renames the fields for consistency and brevity.

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