ofp-util: Update Capabilities for Open Flow 1.2

ofp-util: Update Capabilities for Open Flow 1.2

There are capabilities which are present in one, two and three
of Open Flow 1.0, 1.1 and 1.2. Update OFPC_COMMON to only include
capabilities that are present in all three Open Flow versions and
add ofputil_capabilities_mask() to return the mask of capabilities
for each version.

This does not cover OFPUTIL_C_STP and OFPUTIL_C_GROUP_STATS, which
both use capability bit 3 and are treated as special cases in
ofputil_encode_switch_features() and ofputil_decode_switch_features().

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