ktls_test: Permit connecting to a remote echo server for tests.

[jhb]

Summary

Previously ktls tests always executed over a local socket pair.
ktls.host can be set to a host to connect to with a single socket
instead. The remote end is expected to echo back any data received
(such as the echo service). The port can be set with ktls.port which
defaults to "echo".

This is primarily useful to permit testing NIC TLS offload use cases
where the traffic needs to transit the NIC.

Note that the variables must be set via
'kyua -v test_suites.FreeBSD.ktls.host=host'.

Sponsored by: Chelsio Communications

[markj]

tests/sys/kern/ktls_test.c

180

194

errno will get clobbered before the warning is printed below. So it should be preserved and used with warnc(), or warnx() should be used instead.