This change enables "TCP Fast Open" (TFO) connections to MongoDB.

• The operating system of both the client and server must have TFO support
  • Windows: Server only on Windows 10 or later
  • macOS: Server only on 10.11 or later
  • Linux
    • Client: Kernel version >= 4.11, /proc/sys/net/ipv4/tcp_fastopen set to 1 or 3.
    • Server: Kernel version >= 3.7, /proc/sys/net/ipv4/tcp_fastopen set to 2 or 3

setParameters (these are enabled by default):

• tcpFastOpenClient - Attempt to make outbound TFO connections
• tcpFastOpenServer - Accept inbound TFO connection attempts

Additionally the following setParameter may be tuned on the server:

• tcpFastOpenQueueSize (default 1024)