iwinfo: add "PKG_MIRROR_HASH" to the Makefile

Defining it will let the build tool download the tarball file from
a buildbot server, avoiding a clone of the source repo.

Signed-off-by: Arjun AK <lede@arjunak.com>

package/network/utils/iwinfo/Makefile

@@ -13,6 +13,7 @@ PKG_SOURCE_PROTO:=git
 PKG_SOURCE_URL=$(LEDE_GIT)/project/iwinfo.git
 PKG_SOURCE_DATE:=2017-08-23
 PKG_SOURCE_VERSION:=c1a03e8231a5d8b348b70a182d256725c98a3b0b
+PKG_MIRROR_HASH:=7bd294f50f8ec8c0497c5fbe5527f3ae098814cdfeecf4ccf78a2a8937611664
 PKG_MAINTAINER:=Jo-Philipp Wich <jo@mein.io>
 PKG_LICENSE:=GPL-2.0