openflow-1.1+: OFPT_TABLE_MOD (part 1)

openflow-1.1+: OFPT_TABLE_MOD (part 1)

Added infrastructure to support Openflow OFPT_TABLE_MOD message. This patch
does not include the flexible table miss handling code that is necessary to
support the semantics specified in OFPT_TABLE_MOD messages.

Current flow miss behavior continues to conform to Openflow 1.0.  Future
commits to add more flexible table miss support are needed to fully support
OPFT_TABLE_MOD for Openflow-1.1+.

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