netdev: New function netdev_ref().

I suspect that this makes it easier to make sure that a netdev stays open
as long as needed in some cases where a module needs access to a netdev
opened by some higher-level module.

CC: Ethan Jackson <ethan@nicira.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>
ofp-errors: Fix typos in comment.

Signed-off-by: Ben Pfaff <blp@nicira.com>
ofp-errors: Make ofperr_decode() static.

It had no users outside of ofp-errors.c.

Signed-off-by: Ben Pfaff <blp@nicira.com>
extract-ofp-errors: Remove support for hexadecimal error types.

This feature wasn't used and removing it slightly simplifies the code.

Signed-off-by: Ben Pfaff <blp@nicira.com>
ofp-errors: Implement OpenFlow 1.2+ experimenter error codes.

OpenFlow 1.2 standardized experimenter error codes in a way different from
the Nicira extension.  This commit implements the OpenFlow 1.2+ version.

This commit also makes it easy to add error codes for new experimenter IDs
by adding new *_VENDOR_ID definitions to openflow-common.h.

Signed-off-by: Ben Pfaff <blp@nicira.com>
ofp-errors: New error code ONFBIC_DUP_INSTRUCTION.

This is a prototype of OpenFlow enhancement proposal EXT-260 "Add error
code for duplicate instruction."  It uses the error code proposed there.

Signed-off-by: Ben Pfaff <blp@nicira.com>