RDMA/nldev: Add checks for nla_nest_start() in fill_stat_counter_qps()

RDMA/nldev: Add checks for nla_nest_start() in fill_stat_counter_qps()

[ Upstream commit df579bdc5679557601955578cea4676bd532b00d ]

As the nla_nest_start() may fail with NULL returned, the return value needs
to be checked.

Fixes: f41bb7eb11d4 ("RDMA/netlink: Implement counter dumpit calback")
Signed-off-by: Yuan Can <yuancan@huawei.com>
Link: https://lore.kernel.org/r/20221126043410.85632-1-yuancan@huawei.com
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>