net: use dst_dev_rcu() in sk_setup_caps()

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CVE-2025-40170

In the Linux kernel, the following vulnerability has been resolved: net: use dstdevrcu in sksetupcaps Use RCU to protect accesses to dst-dev from sksetupcaps and skdstgsomaxsize. Also use dstdevrcu in ip6dstmtumaybeforward, and ipdstmtumaybeforward. ip4dsthoplimit can use dstdevnetrcu...