MINOR: stream_interface: add reporting of ressouce allocation errors

SSL and keep-alive will need to be able to fail on allocation errors,
and the stream interface did not allow to report such a cause. The flag
will then be "RC" as already documented.
diff --git a/src/session.c b/src/session.c
index 1183d91..75ac04c 100644
--- a/src/session.c
+++ b/src/session.c
@@ -2576,6 +2576,10 @@
 		err = SN_ERR_SRVCL;
 		fin = SN_FINST_C;
 	}
+	else if (err_type & SI_ET_CONN_RES) {
+		err = SN_ERR_RESOURCE;
+		fin = SN_FINST_C;
+	}
 	else /* SI_ET_CONN_OTHER and others */ {
 		err = SN_ERR_INTERNAL;
 		fin = SN_FINST_C;