MFC 324050
tcp: Don't "negotiate" MSS. _NO_ OSes actually "negotiate" MSS. RFC 879: "... This Maximum Segment Size (MSS) announcement (often mistakenly called a negotiation) ..." This negotiation behaviour was introduced 11 years ago by r159955 without any explaination about why FreeBSD had to "negotiate" MSS: In syncache_respond() do not reply with a MSS that is larger than what the peer announced to us but make it at least tcp_minmss in size. Sponsored by: TCP/IP Optimization Fundraise 2005 The tcp_minmss behaviour is still kept. Syncookie fix was prodded by tuexen, who also helped to test this patch w/ packetdrill. Reviewed by: tuexen, karels, bz (previous version) Sponsored by: Microsoft Differential Revision: https://reviews.freebsd.org/D12430