RDS: Add interface for receive MSG latency trace

RDS: Add interface for receive MSG latency trace

Socket option to tap receive path latency.
SO_RDS: SO_RDS_MSG_RXPATH_LATENCY
with parameter,
struct rds_rx_trace_so {
	u8 rx_traces;
       	u8 rx_trace_pos[RDS_MSG_RX_DGRAM_TRACE_MAX];
}

CMSG:
RDS_CMSG_RXPATH_LATENCY(recvmsg)
Returns rds message latencies in various stages of receive
path in nS. Its set per socket using SO_RDS_MSG_RXPATH_LATENCY
socket option. Legitimate points are defined in
enum rds_message_rxpath_latency. More points can be added in
future.

CSMG format:
struct rds_cmsg_rx_trace {
       	u8 rx_traces;
        u8 rx_trace_pos[RDS_MSG_RX_DGRAM_TRACE_MAX];
       	u64 rx_trace[RDS_MSG_RX_DGRAM_TRACE_MAX];
}

Receive MSG trace points: RDS message Receive Path Latency points
enum rds_message_rxpath_latency {
	RDS_MSG_RX_HDR_TO_DGRAM_START = 0,
	RDS_MSG_RX_DGRAM_REASSEMBLE,
	RDS_MSG_RX_DGRAM_DELIVERED,
	RDS_MSG_RX_DGRAM_TRACE_MAX
}

Tested-by: Namrata Jampani <namrata.jampani@oracle.com>
Reviewed-by: Ajaykumar Hotchandani <ajaykumar.hotchandani@oracle.com>
Reviewed-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Orabug: 22630180
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>