netdev-dpdk: Make memory pool name contain the socket id.

This commit makes the memory pool name contain the socket id.
Since dpdk library do not allow creation of memory pool with
same name, this commit serves as a simple way of making each
name unique.

Signed-off-by: Alex Wang <alexw@nicira.com>
Acked-by: Thomas Graf <tgraf@noironetworks.com>
Acked-by: Pravin B Shelar <pshelar@nicira.com>