net/smc: rdma write inline if qp has sufficient inline space

net/smc: rdma write inline if qp has sufficient inline space

Rdma write with inline flag when sending small packages,
whose length is shorter than the qp's max_inline_data, can
help reducing latency.

In my test environment, which are 2 VMs running on the same
physical host and whose NICs(ConnectX-4Lx) are working on
SR-IOV mode, qperf shows 0.5us-0.7us improvement in latency.

Test command:
server: smc_run taskset -c 1 qperf
client: smc_run taskset -c 1 qperf <server ip> -oo \
		msg_size:1:2K:*2 -t 30 -vu tcp_lat

The results shown below:
msgsize     before       after
1B          11.2 us      10.6 us (-0.6 us)
2B          11.2 us      10.7 us (-0.5 us)
4B          11.3 us      10.7 us (-0.6 us)
8B          11.2 us      10.6 us (-0.6 us)
16B         11.3 us      10.7 us (-0.6 us)
32B         11.3 us      10.6 us (-0.7 us)
64B         11.2 us      11.2 us (0 us)
128B        11.2 us      11.2 us (0 us)
256B        11.2 us      11.2 us (0 us)
512B        11.4 us      11.3 us (-0.1 us)
1KB         11.4 us      11.5 us (0.1 us)
2KB         11.5 us      11.5 us (0 us)

Signed-off-by: Guangguan Wang <guangguan.wang@linux.alibaba.com>
Reviewed-by: Tony Lu <tonylu@linux.alibaba.com>
Tested-by: kernel test robot <lkp@intel.com>
Acked-by: Karsten Graul <kgraul@linux.ibm.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>