This reduces the check-gssmask runtime from around 7min to 1-2sec on
my laptop.
It is, perhaps, suboptimal to disable Nagle for a program that writes
successive 4-byte units of a protocol message in separate syscalls
rather than a single batch, and might be better to instead disable
delayed acks, but:
(a) there's no portable API for disabling delayed acks, and
(b) this program appears to be used exclusively for testing anyway.
fix https://github.com/heimdal/heimdal/issues/1139
