net/smc: transfer fasync_list in case of fallback

SMC does not work together with FASTOPEN. If sendmsg() is called with
flag MSG_FASTOPEN in SMC_INIT state, the SMC-socket switches to
fallback mode. To handle the previous ioctl FIOASYNC call correctly
in this case, it is necessary to transfer the socket wait queue
fasync_list to the internal TCP socket.

Reported-by:  <syzbot+4b1fe8105f8044a26162@syzkaller.appspotmail.com>
Fixes: ee9dfbef

 ("net/smc: handle sockopts forcing fallback")
Signed-off-by: Ursula Braun <ubraun@linux.ibm.com>
Signed-off-by: Karsten Graul <kgraul@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>