drivers: modem: socket: add is_connected field to modem_socket

Let's add a field which the drivers can use to keep track of whether
they are connected or not.  This will normally be enabled / disabled
in the socket connect and URC for socket close notify.

Signed-off-by: Michael Scott <mike@foundries.io>

drivers/modem/modem_socket.c

@@ -238,6 +238,7 @@ void modem_socket_put(struct modem_socket_config *cfg, int sock_fd)
 	sock->sock_fd = -1;
 	sock->is_waiting = false;
 	sock->is_polled = false;
+	sock->is_connected = false;
 	(void)memset(&sock->src, 0, sizeof(struct sockaddr));
 	(void)memset(&sock->dst, 0, sizeof(struct sockaddr));
 

drivers/modem/modem_socket.h

@@ -40,6 +40,7 @@ struct modem_socket {
 	struct k_sem sem_data_ready;
 
 	/** socket state */
+	bool is_connected;
 	bool is_waiting;
 	bool is_polled;