BUG/MINOR: cli: restore "set ssl tls-key" command

in 32af203b75 ("REORG: cli: move ssl CLI functions to ssl_sock.c")
"set ssl tls-key" was accidentally replaced with "set ssl tls-keys"
(keys instead of key). This is undocumented and breaks upgrades from
1.6 to 1.7.

This patch restores "set ssl tls-key" and also registers a helptext.

This should be backported to 1.7.
1 file changed