Add mod_sofia support for setting socket TCP keepalive

Some OSes like linux provide a mechanism for sending TCP keepalive
pings.  Sofia provides its own mechanism for doing this in userspace.
We shouldn't conflate these two mechanisms.

FS-6104

src/mod/endpoints/mod_sofia/mod_sofia.h

@@ -266,6 +266,7 @@ typedef enum {
 	PFLAG_FIRE_MESSAGE_EVENTS,
 	PFLAG_SEND_DISPLAY_UPDATE,
 	PFLAG_RUNNING_TRANS,
+	PFLAG_SOCKET_TCP_KEEPALIVE,
 	PFLAG_TCP_KEEPALIVE,
 	PFLAG_TCP_PINGPONG,
 	PFLAG_TCP_PING2PONG,
@@ -695,6 +696,7 @@ struct sofia_profile {
 	switch_port_t ws_port;
 	char *wss_ip;
 	switch_port_t wss_port;
+	int socket_tcp_keepalive;
 	int tcp_keepalive;
 	int tcp_pingpong;
 	int tcp_ping2pong;