kernel: sctp: Fix null-ptr-deref in reuseport_add_sock().

In the Linux kernel, the following vulnerability has been resolved: sctp: Fix null-ptr-deref in reuseportaddsock. syzbot reported a null-ptr-deref while accessing sk2-skreuseportcb in reuseportaddsock. 0 The repro first creates a listener with SOREUSEPORT. Then, it creates another listener on the...