Attempts to enable or disable pdump in primary process
will fail with core dump because it is not valid to call
rte_mp_request_sync() unless in a secondary process.
Trap the error in the common code used for both enable
and disable requests.
Fixes: 660098d61f57 ("pdump: use generic multi-process channel")
Cc: stable@dpdk.org
Reported-by: Sylvia Grundwürmer <sylvia.grundwuermer@b-plus.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>