samples: pktgen: add missing IPv6 option to pktgen scripts

samples: pktgen: add missing IPv6 option to pktgen scripts

BugLink: https://bugs.launchpad.net/bugs/1946788
[ Upstream commit 0f0c4f1b72e090b23131700bb155944cc28b2a7b ]

Currently, "sample04" and "sample05" are not working properly when
running with an IPv6 option("-6"). The commit 0f06a6787e05 ("samples:
Add an IPv6 "-6" option to the pktgen scripts") has omitted the addition
of this option at "sample04" and "sample05".

In order to support IPv6 option, this commit adds logic related to IPv6
option.

Fixes: 0f06a6787e05 ("samples: Add an IPv6 "-6" option to the pktgen scripts")
Signed-off-by: Juhee Kang <claudiajkang@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Kelsey Skunberg <kelsey.skunberg@canonical.com>