TUN-8161: Fix broken ARM build for armv6

During the recent changes to the build pipeline, the implicit GOARM env variable changed from
6 to 7.
This means we need to explicitly define the GOARM to v6.

Author: joliveirinha

build-packages.sh

@@ -15,6 +15,12 @@ export TARGET_OS=linux
 for arch in ${linuxArchs[@]}; do
     unset TARGET_ARM
     export TARGET_ARCH=$arch
+
+    ## Support for armv6 builds
+    if [[ $arch == arm ]] ; then
+        export TARGET_ARCH=arm
+        export TARGET_ARM=6
+    fi
 
     ## Support for armhf builds 
     if [[ $arch == armhf ]] ; then