ktls.4: note that security/gnutls now supports ktls

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PR: 278083
Sponsored by: ConnectWise
Reviewed by: diizzy
Differential Revision: https://reviews.freebsd.org/D47310

(cherry picked from commit 7200d90644ba61d63e6fec33855bba5d3b7eb7bd)

ktls.4: note that there are multiple openssl ports with KTLS knobs

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Reported by: "Herbert J. Skuhra" <herbert@gojira.at>
Sponsored by: ConnectWise

(cherry picked from commit 1e4da42a36d5cf44bacf0e261626b69a4761f0cc)