DMAC flows should not be programmed for learned SMACs if MAC is in MAC cache

Currently local smac and dmac flows are programmed for learned MACs. The logic should look like this instead:
if this is a vlan/flat provider interface:
program local smac
if the mac doesn't exist in cache
program local dmac

See conversation in comments here:
https://git.opendaylight.org/gerrit/#/c/44619/7/vpnservice/elanmanager/elanmanager-impl/src/main/java/org/opendaylight/netvirt/elan/internal/ElanPacketInHandler.java