mt7601u-openipc: pin the source to a commit instead of HEAD (#2246)

MT7601U_OPENIPC_VERSION was HEAD, so the same tree produced different artifacts
over time and the package could break with no change in this repo. Pin it to an
immutable ref instead.

0ac46553f3190d788b01c15cbeaa14f2951c55a3 is the current tip of openipc/mt7601u
and has been since 2023-08-11, so this is behaviourally a no-op today and purely
protective against future drift. It is also the lineage runtime-verified on a
Hi3518EV200: WPA2 join, RTSP streaming, 15-17 Mbps TX.

The package is enabled in four defconfigs, so this is a live path rather than a
dead one.

Rescoped after review: the original PR also enabled BR2_PACKAGE_MT7601U_OPENIPC
in hi3518ev200_ultimate_defconfig. Per review, firmware images ship WiFi
utilities and not drivers, and per-device selection belongs in Builder, so that
part was dropped on 2026-08-12 and only the pin remains. The changes-requested
predated that rescope and was dismissed as stale, not overridden.

Second instance of an unpinned package found this month; #2316
carries the same fix for atbm60xx. Worth a sweep for other VERSION = HEAD.

Author: phedoreanu

general/package/mt7601u-openipc/mt7601u-openipc.mk

@@ -5,7 +5,7 @@
 ################################################################################
 
 MT7601U_OPENIPC_SITE = $(call github,openipc,mt7601u,$(MT7601U_OPENIPC_VERSION))
-MT7601U_OPENIPC_VERSION = HEAD
+MT7601U_OPENIPC_VERSION = 0ac46553f3190d788b01c15cbeaa14f2951c55a3
 MT7601U_OPENIPC_LICENSE = GPL-2.0
 
 MT7601U_OPENIPC_MODULE_MAKE_OPTS = \