net/smc: Fix memory leak when using percpu refs

This patch adds missing percpu_ref_exit when releasing percpu refs.
When releasing percpu refs, percpu_ref_exit should be called.
Otherwise, memory leak happens.

Fixes: 79a22238 ("net/smc: Use percpu ref for wr tx reference")
Signed-off-by: Kai Shen <KaiShen@linux.alibaba.com>
Reviewed-by: Dust Li <dust.li@linux.alibaba.com>
Reviewed-by: Wenjia Zhang <wenjia@linux.ibm.com>
Link: https://patch.msgid.link/20241010115624.7769-1-KaiShen@linux.alibaba.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>