ofproto: Consider datapath_type when looking for internal ports.

ofproto: Consider datapath_type when looking for internal ports.

Interfaces with type "internal" end up having a netdev with type "tap"
in the dpif-netdev datapath, so a strcmp will fail to match internal
interfaces.

We can translate the types with ofproto_port_open_type() before calling
strcmp to fix this.

This fixes a minor issue where internal interfaces are considered
non-internal in the userspace datapath for the purpose of adjusting the
MTU.

Signed-off-by: Daniele Di Proietto <diproiettod@vmware.com>
Acked-by: Thadeu Lima de Souza Cascardo <cascardo@redhat.com>