This commit contains workaround for a bug known as 'Red Hat issue 1870279'
(connection reset by peer issue in socat versions 1.7.3.3 to 1.7.4.0) which
further causes crashes during SST using mariabackup (when openssl is used).

Also fixed broken logic of automatic generation of the Diffie-Hellman parameters
for socat version less than 1.7.3 (which defaults to 512-bit values instead of
2048-bit ones).