dpdk: Deprecate pdump support.

The conventional way for packet dumping in OVS is to use ovs-tcpdump
that works via traffic mirroring.  DPDK pdump could probably be used
for some lower level debugging, but it is not commonly used for
various reasons.

There are lots of limitations for using this functionality in practice.
Most of them connected with running secondary pdump process and
memory layout issues like requirement to disable ASLR in kernel.
More details are available in DPDK guide:
https://doc.dpdk.org/guides/prog_guide/multi_proc_support.html#multi-process-limitations

Beside the functional limitations it's also hard to use this
functionality correctly.  User must be sure that OVS and pdump utility
are running on different CPU cores, which is hard because non-PMD
threads could float over available CPU cores.  This or any other
misconfiguration will likely lead to crash of the pdump utility
or/and OVS.

Another problem is that the user must actually have this special pdump
utility in a system and it might be not available in distributions.

This change disables pdump support by default introducing special
configuration option '--enable-dpdk-pdump'.  Deprecation warnings will
be shown to users on configuration and in runtime.

Claiming to completely remove this functionality from OVS in one
of the next releases.

Signed-off-by: Ilya Maximets <i.maximets@ovn.org>
Acked-by: Aaron Conole <aconole@redhat.com>
Acked-by: Flavio Leitner <fbl@sysclose.org>
Acked-by: David Marchand <david.marchand@redhat.com>
Signed-off-by: Ian Stokes <ian.stokes@intel.com>

lib/dpdk.c

@@ -434,6 +434,8 @@ dpdk_init__(const struct smap *ovs_other_config)
 
 #ifdef DPDK_PDUMP
     VLOG_INFO("DPDK pdump packet capture enabled");
+    VLOG_WARN("DPDK pdump support is deprecated and "
+              "will be removed in next OVS releases.");
     err = rte_pdump_init(ovs_rundir());
     if (err) {
         VLOG_INFO("Error initialising DPDK pdump");