net: cdc_ncm, cdc_mbim: allow user to prefer NCM for backwards compatibility

commit bd329e1 ("net: cdc_ncm: do not bind to NCM compatible MBIM devices")
introduced a new policy, preferring MBIM for dual NCM/MBIM functions if
the cdc_mbim driver was enabled.  This caused a regression for users
wanting to use NCM.

Devices implementing NCM backwards compatibility according to section
3.2 of the MBIM v1.0 specification allow either NCM or MBIM on a single
USB function, using different altsettings.  The cdc_ncm and cdc_mbim
drivers will both probe such functions, and must agree on a common
policy for selecting either MBIM or NCM.  Until now, this policy has
been set at build time based on CONFIG_USB_NET_CDC_MBIM.

Use a module parameter to set the system policy at runtime, allowing the
user to prefer NCM on systems with the cdc_mbim driver.

Cc: Greg Suarez <[email protected]>
Cc: Alexey Orishko <[email protected]>
Reported-by: Geir Haatveit <[email protected]>
Reported-by: Tommi Kyntola <[email protected]>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=54791
Signed-off-by: Bjørn Mork <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

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