kcm: fix strp_init() order and cleanup

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

kcm: fix strp_init() order and cleanup

strp_init() is called just a few lines above this csk->sk_user_data

check, it also initializes strp->work etc., therefore, it is

unnecessary to call strp_done() to cancel the freshly initialized

work.

And if sk_user_data is already used by KCM, psock->strp should not be

touched, particularly strp->work state, so we need to move strp_init()

after the csk->sk_user_data check.

This also makes a lockdep warning reported by syzbot go away.