Merge branch 'pktgen-samples'

Merge branch 'pktgen-samples'

samples: pktgen: enhance the usability of pktgen samples

This patchset improves the usability of pktgen samples by adding an option for
propagating the environment variable of normal user to sudo. And also adds the
missing IPv6 option to pktgen scripts.

Currently, all pktgen samples are able to use the environment variable instead
of optional parameters. However, it doesn't work appropriately when running
samples as normal user.

This is results of running sample as root and user:

    // running as root
    # DEV=eth0 DEST_IP=10.1.0.1 DST_MAC=00:11:22:33:44:55 ./pktgen_sample01_simple.sh -v -n 1
    Running... ctrl^C to stop

    // running as normal user
    $ DEV=eth0 DEST_IP=10.1.0.1 DST_MAC=00:11:22:33:44:55 ./pktgen_sample01_simple.sh -v -n 1
    [...]
    ERROR: Please specify output device

The reason why passing the environment varaible doesn't work properly when
running samples as normal user is that the environment variable of normal user
doesn't propagate to sudo (root_check_run_with_sudo)). So the first commit
solves this issue by using "-E" (--preserve-env) option of "sudo", which passes
normal user's existing environment variables.

Also, "sample04" and "sample05" are not working properly when running with IPv6
option parameter("-6"). Because the commit 430cace740b8 ("samples: Add an IPv6
"-6" option to the pktgen scripts") has omitted the addition of this option at
these samples. So the second commit adds missing IPv6 option to pktgen scripts.

====================

Fixes: 430cace740b8 ("samples: Add an IPv6 "-6" option to the pktgen scripts")
Signed-off-by: David S. Miller <davem@davemloft.net>