include: Simplify usage of init_le16/32/64 routines

include: Simplify usage of init_le16/32/64 routines

These routines currently just return plain __u16/32/64.  This patch
changes them to return ceph_le16/32/64 types instead.  This has a
number of benefits, in particular it allows the routines to now be
used to directly initialize variables of ceph_le16/32/64 type, as
one would expect from the names of those routines.

This doesn't make much of a difference in the current code base,
but it simplifies future patches to fix endian issues.

Fixes (partially): https://tracker.ceph.com/issues/41605

Signed-off-by: Ulrich Weigand <ulrich.weigand@de.ibm.com>
(cherry picked from commit c576bb28a7744fac6d0bb02cc67c7e6542218e95)
Changes from cherry-picked commit:
- Change in src/msg/msg_types.h (ceph_entity_name) not needed
Signed-off-by: Ulrich Weigand <ulrich.weigand@de.ibm.com>