satellite-sync of RHEL 6 channels fails on Satellite 5.3 and earlier versions

Issue

• Satellite complains that the rhel-x86_64-server-6 channel has incompatible rpm checksum
• unable to sync RHEL 6 channel on Satellite server
• satellite-sync fails with the following error:

# /usr/bin/satellite-sync -c rhel-x86_64-server-6 --debug-level=0
Pushing scout configs to all monitoring scouts
+++ sending log as an email +++

SYNC ERROR:

(Check logs/email for potentially more detail)

Error Message:
   Channel rhel-x86_64-server-6 has incompatible rpm checksum 
(sha-256). Please contact Red Hat support for information about 
upgrading to a newer version of Satellite Server which supports it.
Error Class Code: 3001
Error Class Info: Unable to retrieve channel
Explanation:  
    An error has occurred while processing your request. If this problem
    persists please enter a bug report at bugzilla.redhat.com.
    If you choose to submit the bug report, please be sure to include
    details of what you were trying to do when this error occurred and
    details on how to reproduce this problem.