MINOR: stream_interface: add an init callback to sock_ops

This will be needed for some socket layers such as SSL. It's not used
at the moment.
diff --git a/src/sock_raw.c b/src/sock_raw.c
index 7e0d4c9..4712362 100644
--- a/src/sock_raw.c
+++ b/src/sock_raw.c
@@ -1151,6 +1151,7 @@
 
 /* stream sock operations */
 struct sock_ops sock_raw = {
+	.init    = NULL,
 	.update  = sock_raw_data_finish,
 	.shutr   = sock_raw_shutr,
 	.shutw   = sock_raw_shutw,
diff --git a/src/stream_interface.c b/src/stream_interface.c
index 9dfda93..69db42f 100644
--- a/src/stream_interface.c
+++ b/src/stream_interface.c
@@ -42,6 +42,7 @@
 
 /* socket operations for embedded tasks */
 struct sock_ops stream_int_embedded = {
+	.init    = NULL,
 	.update  = stream_int_update_embedded,
 	.shutr   = stream_int_shutr,
 	.shutw   = stream_int_shutw,
@@ -53,6 +54,7 @@
 
 /* socket operations for external tasks */
 struct sock_ops stream_int_task = {
+	.init    = NULL,
 	.update  = stream_int_update,
 	.shutr   = stream_int_shutr,
 	.shutw   = stream_int_shutw,