tunnel: T2028: prevent single 'remote' keyword
tunnel: T2028: prevent single 'remote' keyword

When the remote keywrod is ommited, the default value of ''
is still set, therefore the ip command will include it.

Remote is now removed if unset.

vyos/vyos-1x,vyos/vyos-1x,vyos/vyos-1x,vyos/vyos-1x