MFC r298769, r299315

MFC r298769, r299315

r298769
=============
tcp/syncache: Set flowid and hash type properly for SYN|ACK

So the underlying drivers can use it to select the sending queue
properly for SYN|ACK instead of rolling their own hash.

Sponsored by:       Microsoft OSTC
Differential Revision:      https://reviews.freebsd.org/D6120

r299315
=============
tcp/syncache: Add comment for syncache_respond

Suggested by:       hiren, hps
Reviewed by:        sbruno
Sponsored by:       Microsoft OSTC
Differential Revision:      https://reviews.freebsd.org/D6148

git-svn-id: svn://svn.freebsd.org/base/stable/10@300004 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f