Revert "xfrm: update SA curlft.use_time"

This reverts commit af734a26.

The abvoce commit is a regression according RFC 2367. A better fix would be
use x->lastused. Which will be propsed later.

according to RFC 2367 use_time == sadb_lifetime_usetime.

"sadb_lifetime_usetime
                   For CURRENT, the time, in seconds, when association
                   was first used. For HARD and SOFT, the number of
                   seconds after the first use of the association until
                   it expires."

Fixes: af734a26 ("xfrm: update SA curlft.use_time")
Signed-off-by: Antony Antony <antony.antony@secunet.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>