Revert "ipv6: Honor all IPv6 PIO Valid Lifetime values"

Revert "ipv6: Honor all IPv6 PIO Valid Lifetime values"

This reverts commit e9b273f6527998e664611e9db2176228a1d6b718.

This commit breaks Linux compatibility with USGv6 tests. The RFC this
commit was based on is actually an expired draft: no published RFC
currently allows the new behaviour it introduced.

Without full IETF endorsement, the flash renumbering scenario this
patch was supposed to enable is never going to work, as other IPv6
equipements on the same LAN will keep the 2 hours limit.

Fixes: e9b273f65279 ("ipv6: Honor all IPv6 PIO Valid Lifetime values")
Signed-off-by: Guillaume Nault <gnault@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>