net: cdc_ncm: remove ncm_parm field

Moving the call to cdc_ncm_setup() after the endpoint
setup removes the last remaining reference to ncm_parm
outside cdc_ncm_setup.

Collecting all the ncm_parm based calculations in
cdc_ncm_setup improves readability.

Cc: Alexey Orishko <alexey.orishko@gmail.com>
Signed-off-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: David S. Miller <davem@davemloft.net>