ovs-ofctl: Merge dump_stats_transaction() into dump_transaction().

ovs-ofctl: Merge dump_stats_transaction() into dump_transaction().

The callers call dump_stats_transaction() for OFPST_* messages and
dump_transaction() for other messages, but the callee can easily
distinguish the two types, so this commit eliminates the difference for the
callers to simplify use.

This will be more valuable in an upcoming commit in which a single
ofputil_encode_*() function can produce an OFPT_* request for some
OpenFlow versions and an OFPST_* request for others.  (Specifically, OF1.4
changes OFPT_QUEUE_GET_CONFIG_REQUEST into OFPST_QUEUE_DESC.)

Also merges dump_trivial_stats_transaction() into
dump_trivial_transaction() for the same reason.

Signed-off-by: Ben Pfaff <blp@ovn.org>
Acked-by: Jarno Rajahalme <jarno@ovn.org>