kernel: net/smc: fix NULL sndbuf_desc in smc_cdc_tx_handler()

In the Linux kernel, the following vulnerability has been resolved: net/smc: fix NULL sndbufdesc in smccdctxhandler When performing a stress test on SMC-R by rmmod mlx5ib driver during the wrk/nginx test, we found that there is a probability of triggering a panic while terminating all link groups...