IB/sa: Fix sa_local_svc_timeout_ms read race

IB/sa: Fix sa_local_svc_timeout_ms read race

When computing the delta, the sa_local_svc_timeout_ms is read without
ib_nl_request_lock held. Though unlikely in practice, this can cause
a race condition if multiple local service threads are managing the
timeout.

Fixes: 2ca546b92a02 ("IB/sa: Route SA pathrecord query through netlink")
Signed-off-by: Vlad Dumitrescu <vdumitrescu@nvidia.com>
Reviewed-by: Mark Zhang <markzhang@nvidia.com>
Signed-off-by: Edward Srouji <edwards@nvidia.com>
Link: https://patch.msgid.link/20250916163112.98414-1-edwards@nvidia.com
Signed-off-by: Leon Romanovsky <leon@kernel.org>