Apply patch for socken listen backlog (FreeBSD)

[Osipov, Michael]

Folks,

a year ago Peter Eriksson [1] provided a decent patch [2] for the listen 
queue overflow on FreeBSD. We have been hit by this too twice today.

I can see that this patch has not been applied. Is there any obstacle 
here? Can we apply this? Shall I provide a PR on GH? We'd need it for at 
least 4.8 or 4.7. 4.9 is not yet available on the FreeBSD ports tree.

Regards,

Michael

[1] https://lists.samba.org/archive/samba/2018-January/213321.html
[2] 
https://people.ifm.liu.se/peter/patches/samba/socket_listen_backlog.patch