nvmeof-mp/001: Set expected count properly

nvmeof-mp/001: Set expected count properly

The number of block devices will increase according
to the number of RDMA-capable NICs.
For example, nvmeof-mp/001 with two RDMA-capable NICs
got the following error:
-------------------------------------
    Configured NVMe target driver
    -count_devices(): 1 <> 1
    +count_devices(): 2 <> 1
    Passed
-------------------------------------

Set expected count properly by calculating the number
of RDMA-capable NICs.

Signed-off-by: Xiao Yang <yangx.jy@fujitsu.com>
Reviewed-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>