dcb: Use ifindex instead of ifname

Use ifindex instead of ifname in the DCB app ring. This makes for a smaller
data structure and faster comparisons. It also avoids possible issues when
a net device is renamed.

Signed-off-by: Mark Rustad <mark.d.rustad@intel.com>
Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>