net: wwan: core: spell port device name in lowercase

Usually a device name is spelled in lowercase, let us follow this
practice in the WWAN subsystem as well. The bottom line is that such
name is easier to type.

To keep the device type attribute contents more natural (i.e., spell
abbreviations in uppercase), while making the device name lowercase,
turn the port type strings array to an array of structure that contains
both the port type name and the device name suffix.

Signed-off-by: Sergey Ryazanov <ryazanov.s.a@gmail.com>
Reviewed-by: Loic Poulain <loic.poulain@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>