RDMA/core: reduce stack using in nldev_stat_get_doit()

RDMA/core: reduce stack using in nldev_stat_get_doit()

In the s390 defconfig, gcc-10 and earlier end up inlining three functions
into nldev_stat_get_doit(), and each of them uses some 600 bytes of stack.

The result is a function with an overly large stack frame and a warning:

drivers/infiniband/core/nldev.c:2466:1: error: the frame size of 1720 bytes is larger than 1280 bytes [-Werror=frame-larger-than=]

Mark the three functions noinline_for_stack to prevent this, ensuring
that only one copy of the nlattr array is on the stack of each function.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://patch.msgid.link/20250620113335.3776965-1-arnd@kernel.org
Signed-off-by: Leon Romanovsky <leon@kernel.org>