nx-match: Refactor nxm_put_ip() to handle all IPv4 and IPv6 fields.

Until now, some fields have been handled in the caller, and the caller has
been responsible for distinguishing ICMPv4 from ICMPv6.  This
implementation seems to make the code a little easier to understand.

Signed-off-by: Ben Pfaff <blp@nicira.com>
meta-flow: Encode OXM version information into the flow table.

Signed-off-by: Ben Pfaff <blp@nicira.com>
meta-flow: Use OXM-defined constant for TCP flags in OpenFlow 1.5.

This also adds the definitions of a few other OXM headers we didn't have
yet.

EXT-109.
Signed-off-by: Ben Pfaff <blp@nicira.com>