up_dump_prefix() should not clear the p->flags before possibly calling

up_dump_prefix() should not clear the p->flags before possibly calling
prefix_adjout_destroy(). Doing so will restult in a double pt_unref()
call because prefix_adjout_destroy() no longer notices that the prefix
was an actuall withdraw and wrongly calls prefix_unlink().
For updates the PREFIX_FLAG_UPDATE flag needs to be cleared after
removing the prefix from the update RB tree.
Adjust the EoR codepath in a similar way. EoR have a NULL pt_entry and
so prefix_adjout_destroy() is unable to do the RB_REMOVE.
This fixes the regress errors reported by anton@
OK tb@