BUG/MEDIUM: peers: trash of expired entries delayed after fullresync

BUG/MEDIUM: peers: trash of expired entries delayed after fullresync

stksess_new has set the entry expire to the table expire delay,
if it is a new entry, set_entry inserts at that position in the expire
tree. There was a touch_remote updating the expire setting but the
tree's re-ordering is not designed to set back in the past resulting
to an entry that will be trashed only after a full table's expire delay
regardless the expire set on the stktsess.

This patch sets the newts expire before the call of 'set_entry'.
This way a new inserted entry is set directly at the right position
in the tree to trash the entry in time.

This patch should be backported on all supported branches and at
least v2.8