Our conn.Bind implementation is updated to make Send() offset-aware for
future VXLAN/Geneve encapsulation support.
Updates tailscale/corp#27502
Signed-off-by: Jordan Whited <jordan@tailscale.com>
This commit adds a batchingConn interface, and renames batchingUDPConn
to linuxBatchingConn. tryUpgradeToBatchingConn() may return a platform-
specific implementation of batchingConn. So far only a Linux
implementation of this interface exists, but this refactor is being
done in anticipation of a Windows implementation.
Updates tailscale/corp#21874
Signed-off-by: Jordan Whited <jordan@tailscale.com>
