RDS: Add support for per socket SO_TIMESTAMP for incoming messages

RDS: Add support for per socket SO_TIMESTAMP for incoming messages

The SO_TIMESTAMP generates time stamp for each incoming RDS message
using the wall time. Result is returned via recv_msg() in a control
message as timeval (usec resolution).

User app can enable it by using SO_TIMESTAMP setsocketopt() at
SOL_SOCKET level. CMSG data of cmsg type SO_TIMESTAMP contains the
time stamp in struct timeval format.

Orabug: 22190837

Acked-by: Ajaykumar Hotchandani <ajaykumar.hotchandani@oracle.com>
Acked-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Reviewed-by: Shamir Rabinovitch <shamir.rabinovitch@oracle.com>
Tested-by: Namrata Jampani <namrata.jampani@oracle.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>