eal/freebsd: lock memory device to prevent conflicts

eal/freebsd: lock memory device to prevent conflicts

Only a single DPDK process on the system can be using the /dev/contigmem
mappings at a time, but this was never explicitly enforced, e.g. when
using --in-memory flag on two processes. To prevent possible conflict
issues, we lock the dev node when it's in use, preventing other DPDK
processes from starting up and causing problems for us.

Fixes: 764bf26873b9 ("add FreeBSD support")
Cc: stable@dpdk.org
Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Reviewed-by: Anatoly Burakov <anatoly.burakov@intel.com>