[CONNECTOR]: Cleanup struct cn_callback_entry

- 'cb' is a fake struct member. In a previous patch struct cn_callback
was renamed to cn_callback_id, so 'cb' should have been deleted at that
time.

- 'nls' isn't used and is redundant, we can retrieve this data through
cn_callback_entry.pdev->nls.

- 'seq' and 'group' should be u32, as they are declared to be u32 in
other places.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>