knot-resolver6: Fix meson include path

This include was broken during packaging of the manager on Turris OS 6.x
where the include was in different path and then the final merge was
into Turris 7.0 but path was not adjusted correctly.

net/knot-resolver6/Makefile

@@ -31,7 +31,7 @@ PYTHON3_PKG_BUILD:=0
 Hooks/Configure/Post+=Py3Build/FindStdlibDepends
 
 include $(INCLUDE_DIR)/package.mk
-include $(TOPDIR)/feeds/packages/devel/meson/meson.mk
+include $(INCLUDE_DIR)/meson.mk
 include $(TOPDIR)/feeds/packages/lang/python/python3-package.mk
 
 define Package/knot-resolver6