net: vmw_vsock: vmci: Check memcpy_from_msg()

vmci_transport_dgram_enqueue() does not check the return value
of memcpy_from_msg().  If memcpy_from_msg() fails, it is possible that
uninitialized memory contents are sent unintentionally instead of user's
message in the datagram to the destination.  Return with an error if
memcpy_from_msg() fails.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 0f7db23a ("vmci_transport: switch ->enqeue_dgram, ->enqueue_stream and ->dequeue_stream to msghdr")
Signed-off-by: Artem Chernyshev <artem.chernyshev@red-soft.ru>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Reviewed-by: Vishnu Dasa <vdasa@vmware.com>
Signed-off-by: David S. Miller <davem@davemloft.net>