CVE-2021-47624 net/sunrpc: fix reference count leaks in rpc_sysfs_xprt_state_change

In the Linux kernel, the following vulnerability has been resolved:

net/sunrpc: fix reference count leaks in rpc_sysfs_xprt_state_change

The refcount leak issues take place in an error handling path. When the
3rd argument buf doesn’t match with “offline”, “online” or “remove”, the
function simply returns -EINVAL and forgets to decrease the reference
count of a rpc_xprt object and a rpc_xprt_switch object increased by
rpc_sysfs_xprt_kobj_get_xprt() and
rpc_sysfs_xprt_kobj_get_xprt_switch(), causing reference count leaks of
both unused objects.

Fix this issue by jumping to the error handling path labelled with
out_put when buf matches none of “offline”, “online” or “remove”.