refcount_t type and corresponding API can protect refcounters from
accidental underflow and overflow and further use-after-free situations.

Link: https://lore.kernel.org/r/1626674454-56075-1-git-send-email-xiyuyang19@fudan.edu.cnSigned-off-by: NXiyu Yang <xiyuyang19@fudan.edu.cn>
Signed-off-by: NXin Tan <tanxin.ctf@gmail.com>
Tested-by: NJosh Fisher <josh.fisher@cornelisnetworks.com>
Acked-by: NDennis Dalessandro <dennis.dalessandro@cornelisnetworks.com>
Signed-off-by: NJason Gunthorpe <jgg@nvidia.com>