ip: expose inet sockopts through inet_diag

Expose all exisiting inet sockopt bits through inet_diag for debug purpose.
Corresponding changes in iproute2 ss will be submitted to output all
these values.

Signed-off-by: Wei Wang <weiwan@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Mahesh Bandewar <maheshb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>