net: cdc_ncm: split .bind device initialization

Now that we have split out the part of the device setup
which MUST be done with the data interface in altsetting 0,
we can delay the rest of the initialization. This allows us
to move some of post-init buffer size config from bind to
the appropriate setup function.

The purpose of this refactoring is to collect all code
adjusting the rx_max and tx_max buffers in one place, so
that it is easier to call it from multiple call sites.

Signed-off-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: David S. Miller <davem@davemloft.net>