Ignore "unsupported frontend protocol" error on Centos/RHEL 6.
Ignore "unsupported frontend protocol" error on Centos/RHEL 6.

The unsupported version error is showing up on older versions of PostgreSQL (e.g. 9.1, 9.2) on RHEL6 when setting up a standby with streaming replication. The error occurs when a client does not properly send a version number and it's not clear why it is happening here, but it does not appear to have anything to do with pgBackRest and only affects RHEL6, i.e. 9.1 and 9.2 do not show this error on other distros.

For now ignore the error since RHEL6 is nearly EOL.

pgbackrest/pgbackrest,pgmasters/backrest,pgbackrest/pgbackrest,pgmasters/backrest,pgbackrest/pgbackrest