socket: Add Support for TCP keep alive variables

socket: Add Support for TCP keep alive variables

The tcp keep alive variables now can be configured via conf
parameter. Follwing variables are now supported by this patch.

tcp_keepalive_intvl: The number of seconds between TCP keep-alive probes

tcp_keepalive_probes: The maximum number of TCP keep-alive probes to
send before giving up and killing the connection if no response is
obtained from the other end.

tcp_keepalive_time: The number of seconds a connection needs to be
idle before TCP begins sending out keep-alive probes.