net/smc: support SMC-R V2 for rdma devices with max_recv_sge equals to 1

net/smc: support SMC-R V2 for rdma devices with max_recv_sge equals to 1

For SMC-R V2, llc msg can be larger than SMC_WR_BUF_SIZE, thus every
recv wr has 2 sges, the first sge with length SMC_WR_BUF_SIZE is for
V1/V2 compatible llc/cdc msg, and the second sge with length
SMC_WR_BUF_V2_SIZE-SMC_WR_TX_SIZE is for V2 specific llc msg, like
SMC_LLC_DELETE_RKEY and SMC_LLC_ADD_LINK for SMC-R V2. The memory
buffer in the second sge is shared by all recv wr in one link and
all link in one lgr for saving memory usage purpose.

But not all RDMA devices with max_recv_sge greater than 1. Thus SMC-R
V2 can not support on such RDMA devices and SMC_CLC_DECL_INTERR fallback
happens because of the failure of create qp.

This patch introduce the support for SMC-R V2 on RDMA devices with
max_recv_sge equals to 1. Every recv wr has only one sge with individual
buffer whose size is SMC_WR_BUF_V2_SIZE once the RDMA device's max_recv_sge
equals to 1. It may use more memory, but it is better than
SMC_CLC_DECL_INTERR fallback.

Co-developed-by: Wen Gu <guwen@linux.alibaba.com>
Signed-off-by: Wen Gu <guwen@linux.alibaba.com>
Signed-off-by: Guangguan Wang <guangguan.wang@linux.alibaba.com>
Reviewed-by: Wenjia Zhang <wenjia@linux.ibm.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>