net: implement IsConnectionBrokenError for Plan 9

Author: erenberg

net/error_plan9.go

@@ -0,0 +1,10 @@
+//go:build plan9
+// +build plan9
+
+package net
+
+// Check if error returned by operation on a socket failed because
+// the other side has closed the connection.
+func IsConnectionBrokenError(err error) bool {
+	return false
+}