vhost: remove switching related logics

vhost: remove switching related logics

The following logics will be moved to vhost example:
 1. mac learning, which is used to learn the mac address from the first
transmitted packet of guest and bind the vhost device to a queue in a
pool of VMDQ.
 2. VMDQ mac/vlan filter: Each pool the vhost device is bind to is
assigned a mac/vlan filter.
 3. num_devices is used to specify the maximum vhost devices the nic supports.

Signed-off-by: Huawei Xie <huawei.xie@intel.com>
Acked-by: Changchun Ouyang <changchun.ouyang@intel.com>