Bluetooth: MGMT: iterate over mesh commands in mgmt_mesh_foreach()

In 'mgmt_mesh_foreach()', iterate over mesh commands
rather than generic mgmt ones. Compile tested only.

Fixes: b338d917 ("Bluetooth: Implement support for Mesh")
Signed-off-by: Dmitry Antipov <dmantipov@yandex.ru>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>