ofproto: Add table config to struct ofproto

Add table config to to struct ofproto and set it
when a table mod message is received.

This is in preparation for changing the behaviour of the switch
based on table config.

Cc: Andy Zhou <azhou@nicira.com>
Signed-off-by: Simon Horman <horms@verge.net.au>
Signed-off-by: Ben Pfaff <blp@nicira.com>