client: Fix libcephfs aio metadata corruption.

client: Fix libcephfs aio metadata corruption.

Problem:
With cephfs nfs-ganesha, there were following
asserts hit while doing write on a file.

1. FAILED ceph_assert((bool)_front == (bool)_size)
2. FAILED ceph_assert(cap_refs[c] > 0)

Cause:
In aio path, the client_lock was not being held
in the internal callback after the io is done where
it's expected to be taken leading to corruption.

Fix:
Take client_lock in the callback

Fixes: https://tracker.ceph.com/issues/68146
Signed-off-by: Kotresh HR <khiremat@redhat.com>