[build]: Use zstd compression for base filesystem squashfs

Signed-off-by: Saikrishna Arcot <[email protected]>

build_debian.sh

@@ -585,7 +585,7 @@ sudo rm -f $ONIE_INSTALLER_PAYLOAD $FILESYSTEM_SQUASHFS
 sudo du -hsx $FILESYSTEM_ROOT
 sudo mkdir -p $FILESYSTEM_ROOT/var/lib/docker
 scripts/collect_host_image_version_files.sh $TARGET_PATH $FILESYSTEM_ROOT
-sudo mksquashfs $FILESYSTEM_ROOT $FILESYSTEM_SQUASHFS -e boot -e var/lib/docker -e $PLATFORM_DIR
+sudo mksquashfs $FILESYSTEM_ROOT $FILESYSTEM_SQUASHFS -comp zstd -b 1M -e boot -e var/lib/docker -e $PLATFORM_DIR
 
 # Ensure admin gid is 1000
 gid_user=$(sudo LANG=C chroot $FILESYSTEM_ROOT id -g $USERNAME) || gid_user="none"