RDMA/iwcm: Don't copy past the end of dev_name() string

We now use dev_name(&ib_device->dev) instead of ib_device->name in iwpm
messages.  The name field in struct device is a const char *, where as
ib_device->name is a char array of size IB_DEVICE_NAME_MAX, and it is
pre-initialized to zeros.

Since iw_cm_map() was using memcpy() to copy in the device name, and
copying IWPM_DEVNAME_SIZE bytes, it ends up copying past the end of the
source device name string and copying random bytes.  This results in iwpmd
failing the REGISTER_PID request from iwcm.  Thus port mapping is broken.

Validate the device and if names, and use strncpy() to inialize the entire
message field.

Fixes: 896de009 ("RDMA/core: Use dev_name instead of ibdev->name")
Cc: stable@vger.kernel.org
Signed-off-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>