Merge branch 'tcp-fastopen-observability'

Jeremy Harris says:

====================
tcp: fastopen: observability

Whether TCP Fast Open was used for a connection is not reliably
observable by an accepting application when the SYN passed no data.

Fix this by noting during SYN receive processing that an acceptable Fast
Open option was used, and provide this to userland via getsockopt TCP_INFO.
====================

Link: https://patch.msgid.link/20250423124334.4916-1-jgh@exim.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>