RDMA/iw_cxgb4: clean up c4iw_reject_cr()

Get rid of unneeded code, and refactor things a bit.

For MPA version 0 we abort the connection.  For > 0, we attempt to send
an MPA_START/REJECT Reply, and then disconnect gracefully.  If the send
of the MPA message fails, then we abort the connection.  We can ignore
c4iw_ep_disconnect() errors here because it will clean up the endpoint
if there are failures.

Signed-off-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Hariprasad Shenai <hariprasad@chelsio.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>