My borntraeger@de.ibm.com email is just a forwarder to the
linux.ibm.com address. Let us remove the extra hop to avoid
a potential source of errors.

While at it, add the relevant email addresses to mailmap.

Signed-off-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Message-Id: <20211126102449.287524-1-borntraeger@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>