ovn-controller: Drop unknown datapath log message.

This patch emits a log message that is encountered a lot under normal
circumstances.  For example, I'm seeing it almost 20,000 times in a
test run of the OpenStack test suite and hundreds of times while doing
basic tasting under ovs-sandbox.

ovn-controller keeps a hash of logical data paths that have ports
associated with them (logical_datapaths).  This message occurs when
looping through all Pipeline entries and a Pipeline's logical datapath
does not exist in this hash.  However, a logical switch with no ports
will have entries in the Pipeline table, but nothing in Bindings (and
not end up in the logical_datapaths hash).  Currently, this message
will be emitted 6 times for every logical switch without any logical
ports every time the ovn-controller main loop comes around and runs
this code.  Instead, the right thing to do to silently ignore the
pipeline entry, because there's nothing useful to be done with it.

Signed-off-by: Russell Bryant <rbryant@redhat.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>

ovn/controller/pipeline.c

@@ -270,10 +270,6 @@ pipeline_run(struct controller_ctx *ctx)
         const struct logical_datapath *ldp;
         ldp = ldp_lookup(&pipeline->logical_datapath);
         if (!ldp) {
-            static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 1);
-            VLOG_INFO_RL(&rl,
-                         "logical flow for unknown logical datapath "UUID_FMT,
-                         UUID_ARGS(&pipeline->logical_datapath));
             continue;
         }