sdp: Fix data corretness regression test failure.

sdp: Fix data corretness regression test failure.

Mellanox regression testing for data correctness started failing
after the recent addition of bzcopy. This was because sdp_sendmsg
returned before all in-flight RC transfers completed.
This allowed user space to modify buffers that had not been sent.

A big oops.

This fixes that bug.  Small frame bandwidth is even worse
now, but small frame latency is lower which is good.  The
default transfer size that triggers bzcopy has been
increased to the bandwidth crossover point found in
MLX4-MLX4 tests.  More work will be required to find the
best value for the release.

Signed-off-by: Jim Mott <jim@mellanox.com>