nvmeof: Change the NVMEOF image version to 1.6

nvmeof: Change the NVMEOF image version to 1.6
Fixes: https://tracker.ceph.com/issues/75097
Signed-off-by: Gil Bregman <gbregman@il.ibm.com>
(cherry picked from commit 02587347b0a4e7ae1d7f5d738bd33808e2d56bc9)
Signed-off-by: Gil Bregman <gbregman@il.ibm.com>
Conflicts:

    src/python-common/ceph/cephadm/images.py

We forgot to set version 1.6 in time. By the time we got to it, the main
branch has already moved up to use version 1.7 which contains features
we don't have in tentacle. We want version 1.6 for tentacle so we had to
change the commit here to 1.6.

Signed-off-by: Gil Bregman <gbregman@il.ibm.com>