net/virtio: adapt virtio-user status size
net/virtio: adapt virtio-user status size

Set proper payload size for set/get status message. The payload
size varies according to backend types.

Signed-off-by: Maxime Coquelin <9a2667dee3b90866bbc9c2696cff2b7d5616c95a@redhat.com>
Signed-off-by: Patrick Fu <9a0e5a62d6df51dec9c1e0dc80b22878833f5aba@intel.com>
Reviewed-by: Chenbo Xia <5d298a4585cd22ca5d29de25967a5599c4c324c8@intel.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk