Fast track MFC r228016:
Plug a TCP reassembly UMA zone leak introduced in r226228 by only using the
backup stack queue entry when the zone is exhausted, otherwise we leak a zone
allocation each time we plug a hole in the reassembly queue.
Reported by: many on freebsd-stable@ (thread: "TCP Reassembly Issues")
Tested by: many on freebsd-stable@ (thread: "TCP Reassembly Issues")
Reviewed by: bz (very brief sanity check)
Approved by: re (kib)
git-svn-id: svn://svn.freebsd.org/base/releng/9.0@228059
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