ip6: fix off-by-one in pltime and vltime expiration checks

[zarychtam_plan-b.pwste.edu.pl]

Summary

Fix an off-by-one error in IFA6_IS_DEPRECATED() and IFA6_IS_INVALID().

Previously, the macros used '>' instead of '>=' when comparing elapsed
time against the preferred and valid lifetimes. This caused any deprecated
address to become usable again for one extra second after receiving each
Router Advertisement. In that short window, the address could be
selected as a source for outgoing connections.

Update the checks to use '>=' so that addresses are deprecated or
invalid when their lifetime expires.

PR: 289177
Reported by: Dmitry Nexus <[e-mail]>

[ae]

LGTM.

[zlei]

Looks good to me.

To simplify the evaluation if the if addr is deprecated or invalid, just think of 0 value of ia6t_pltime and ia6t_vltime . A 0 life time means the addr immediately reach EoL.