RDMA/siw: work around clang stack size warning

RDMA/siw: work around clang stack size warning

clang inlines a lot of functions into siw_qp_sq_process(), with the
aggregate stack frame blowing the warning limit in some configurations:

drivers/infiniband/sw/siw/siw_qp_tx.c:1014:5: error: stack frame size (1544) exceeds limit (1280) in 'siw_qp_sq_process' [-Werror,-Wframe-larger-than]

The real problem here is the array of kvec structures in siw_tx_hdt that
makes up the majority of the consumed stack space.

Ideally there would be a way to avoid allocating the array on the
stack, but that would require a larger rework. Add a noinline_for_stack
annotation to avoid the warning for now, and make clang behave the same
way as gcc here. The combined stack usage is still similar, but is spread
over multiple functions now.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://patch.msgid.link/20250620114332.4072051-1-arnd@kernel.org
Reviewed-by: Zhu Yanjun <yanjun.zhu@linux.dev>
Acked-by: Bernard Metzler <bmt@zurich.ibm.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>