Replace local patch with fix from upstream

Cherry-pick:

>From e2a2a24a8e78427ff8667d625f5befbe88c328bb Mon Sep 17 00:00:00 2001
From: Kamil Rytarowski <n54@gmx.com>
Date: Wed, 23 Sep 2020 04:20:05 +0200
Subject: [PATCH] Preinitialize the sockaddr_un variable to zero

Don't pass random sun_len for the BSD's,
zero the whole structure as recommended for portability.

Reported by Coverity.

gdbsupport/ChangeLog:

* agent.cc (gdb_connect_sync_socket): Preinitialize addr with zeros.

(kamil)