netcat: add --crlf to convert LF into CRLF

This adds the --crlf option to netcat, which triggers translation of \n
characters into \r\n sequences in the input -> network direction.
The Linux version of nc also supports this functionality with --crlf and
-C. The OpenBSD version uses -C to specify client certificates. Our
version is too old and doesn't have it, but I avoided adding -C anyway
to ease future syncs with upstream.

Attempts to upstream the feature were unsuccessful:
https://marc.info/?t=169282068500001

Differential Revision: https://reviews.freebsd.org/D41489