TLS 1.3 clarifies that a ticket lifetime of zero means the session is
unusable. We don't currently pay attention to that field (to be fixed in
later changes) but, in preparation for this, switch the >= to a >.
Change-Id: I0e67a0d97bc8def04914f121e84d3e7a2d640d2c
Reviewed-on: https://boringssl-review.googlesource.com/12102
Commit-Queue: David Benjamin <davidben@google.com>
Reviewed-by: Adam Langley <agl@google.com>