netprio_cgroup: Use memcpy instead of the for-loop to copy priomap

Replace the current (inefficient) for-loop with memcpy, to copy priomap.

Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>