socket: return in->hdr to smalloc pool

commit bc64420 introduced an extra smalloc for the in->hdr,
however it did use iscsi_free instead of iscsi_sfree to free it.

Signed-off-by: Peter Lieven <pl@kamp.de>

lib/socket.c

@@ -979,7 +979,7 @@ static int iscsi_tcp_queue_pdu(struct iscsi_context *iscsi,
 void
 iscsi_free_iscsi_in_pdu(struct iscsi_context *iscsi, struct iscsi_in_pdu *in)
 {
-	iscsi_free(iscsi, in->hdr);
+	iscsi_sfree(iscsi, in->hdr);
 	iscsi_free(iscsi, in->data);
 	in->data=NULL;
 	iscsi_sfree(iscsi, in);