selftests: fib_tests: add temporary IPv6 address renewal test

selftests: fib_tests: add temporary IPv6 address renewal test

Add a test to check that temporary IPv6 address is regenerated properly
after the base prefix is deprecated and restored.

Fib6 temporary address renewal test
    TEST: IPv6 temporary address cleanly deprecated and regenerated     [ OK ]

Signed-off-by: Fernando Fernandez Mancera <fmancera@suse.de>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://patch.msgid.link/20260523103811.3790-2-fmancera@suse.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>