RDMA/nldev: Allow different fill function per resource

So far res_get_common_{dumpit, doit} was using the default resource fill
function which was defined as part of the nldev_fill_res_entry
fill_entries.

Add a fill function pointer as an argument allows us to use different fill
function in case we want to dump different values then 'rdma resource'
flow do, but still use the same existing general resources dumping flow.

Link: https://lore.kernel.org/r/20191016062308.11886-3-leon@kernel.org


Signed-off-by: Erez Alfasi <ereza@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>