ceph: save cap_auths in MDS client when session is opened

Save the cap_auths, which have been parsed by the MDS, in the opened
session.

[ idryomov: use s64 and u32 instead of int64_t and uint32_t, switch to
            bool for root_squash, readable and writeable ]

Link: https://tracker.ceph.com/issues/61333


Signed-off-by: Xiubo Li <xiubli@redhat.com>
Reviewed-by: Milind Changire <mchangir@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>