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.

build-packages.sh

@@ -16,6 +16,12 @@ 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
         export TARGET_ARCH=arm