Merge pull request #17513 from Liuchang0812/wip-max-avail-in-df

mon: incorrect MAX AVAIL in "ceph df"

Reviewed-by: Kefu Chai <kchai@redhat.com>
Reviewed-by: Sage Weil <sage@redhat.com>

diff --cc src/mon/PGMap.cc
Simple merge

diff --cc src/test/mon/PGMap.cc
Simple merge