macvtap: signal truncated packets

macvtap: signal truncated packets

macvtap_put_user() never return a value grater than iov length, this in fact
bypasses the truncated checking in macvtap_recvmsg(). Fix this by always
returning the size of packet plus the possible vlan header to let the trunca
checking work.

Cc: Vlad Yasevich <[email protected]>
Cc: Zhi Yong Wu <[email protected]>
Cc: Michael S. Tsirkin <[email protected]>
Signed-off-by: Jason Wang <[email protected]>
Acked-by: Vlad Yasevich <[email protected]>
Acked-by: Michael S. Tsirkin <[email protected]>
Signed-off-by: David S. Miller <[email protected]>