Not every CLC proposal message needs the maximum buffer length.
Due to the MSG_WAITALL flag, it is important to use the peeked
real length when receiving the message.

Fixes: d63d271c ("smc: switch to sock_recvmsg()")
Signed-off-by: NUrsula Braun <ubraun@linux.vnet.ibm.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>