RDMA/nes: Fix CX4 link problem in back-to-back configuration

Commit 09124e19 ("RDMA/nes: Add support for KR device id 0x0110") took
out too much code and broke CX4 link detection in back-to-back
configuration.  Put back the code that does the link check.

Signed-off-by: Chien Tung <chien.tin.tung@intel.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>