ofproto: Implement OF1.4 error code for set-async-config

ofproto: Implement OF1.4 error code for set-async-config

This patch adds support for Openflow1.4 error codes for set-async-config.
In this patch, a new error type, OFPET_ASYNC_CONFIG_FAILED is introduced
that enables the switch to properly inform the controller when controller
tries to set invalid mask or unsupported configuration.

Signed-off-by: Ambika Arora <ambika.arora@tcs.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>