mem: improve parameter checking on memory hotplug

mem: improve parameter checking on memory hotplug

Currently, we don't check anything that comes in through memory hotplug
subsystem using the IPC, because we always assume the data is correct.
This is okay as anyone having access to the IPC socket would also have
rights to crash the DPDK process through other means, but it's still a
good practice to do parameter checking, so fix the code to do that.

Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>