MFH: r424592
Bring in upstream commit ec165c392ca54317dbe3064a8c200de6531e89ad:
Unregister the KEXINIT handler after message has been received. Otherwise an unauthenticated peer can repeat the KEXINIT and cause allocation of up to 128MB -- until the connection is closed. Reported by shilei-c at 360.cn
Security: CVE-2016-8858
Approved by: ports-secteam (with hat)