4726.	[port]		Prevent setsockopt() errors related to TCP_FASTOPEN
			from being logged on FreeBSD if the kernel does not
			support it.  Notify the user when the kernel does
			support TCP_FASTOPEN, but it is disabled by sysctl.
			Add a new configure option, --disable-tcp-fastopen, to
			disable use of TCP_FASTOPEN altogether. [RT #44754]