MINOR: ssl: add a new global option "tune.ssl.hard-maxrecord"

MINOR: ssl: add a new global option "tune.ssl.hard-maxrecord"

Low footprint client machines may not have enough memory to download a
complete 16KB TLS record at once. With the new option the maximum
record size can be defined on the server side.

Note: Before limiting the the record size on the server side, a client should
consider using the TLS Maximum Fragment Length Negotiation Extension defined
in RFC6066.

This patch fixes GitHub issue #1679.