ovs-numa: Introduce function to set current thread affinity.

ovs-numa: Introduce function to set current thread affinity.

This commit moves the code that sets the pmd threads affinity from
netdev-dpdk to ovs-numa.  There's one small part left in netdev-dpdk, to
set the lcore_id.

Now dpif-netdev will call both modules (ovs-numa and netdev-dpdk) when
starting a pmd thread.

This change will allow having a dummy implementation of the set affinity
call, for testing purposes.

Signed-off-by: Daniele Di Proietto <diproiettod@vmware.com>
Acked-by: Ilya Maximets <i.maximets@samsung.com>