Usage of send buffer "sndbuf" is synced
(a) before filling sndbuf for cpu access
(b) after filling sndbuf for device access

Usage of receive buffer "RMB" is synced
(a) before reading RMB content for cpu access
(b) after reading RMB content for device access
Signed-off-by: NUrsula Braun <ubraun@linux.vnet.ibm.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>