LU-16822 tests: Setup IPv6 with fake network device

LU-16822 tests: Setup IPv6 with fake network device

Several of the LNet sanity test create a fake network device and
setup an IP. Only a IPv4 was setup so also setup a IPv6 address
to increase the testing coverage for large NID support.

Test-Parameters: trivial testlist=sanity-lnet
Change-Id: If29adf74f1fe6449ad3f48663c2872a39bf4664c
Signed-off-by: James Simmons <jsimmons@infradead.org>
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/53599
Reviewed-by: Chris Horn <chris.horn@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Frank Sehr <fsehr@whamcloud.com>
Reviewed-by: Serguei Smirnov <ssmirnov@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>