t_client.sh: do not require fping6

t_client.sh: do not require fping6

fping and fping6 were merged in version 4.0,
released in 2017. Many recent distributions do
not include the compatibility symlink anymore.

So if we find fping but not fping6 do not error
out but assume that fping is capable of IPv6.

Signed-off-by: Frank Lichtenheld <frank@lichtenheld.com>
Acked-by: Antonio Quartulli <a@unstable.cc>
Message-Id: <20220822141806.39406-1-frank@lichtenheld.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg25058.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>