net/smc: use sk_rcvbuf as start for rmb creation

Commit 3e034725 ("net/smc: common functions for RMBs and send buffers")
merged handling of SMC receive and send buffers. It introduced sk_buf_size
as merged start value for size determination. But since sk_buf_size is not
used at all, sk_sndbuf is erroneously used as start for rmb creation.
This patch makes sure, sk_buf_size is really used as intended, and
sk_rcvbuf is used as start value for rmb creation.

Fixes: 3e034725

 ("net/smc: common functions for RMBs and send buffers")
Signed-off-by: Ursula Braun <ubraun@linux.vnet.ibm.com>
Reviewed-by: Hans Wippel <hwippel@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>