modemmanager: add config optional netifd integration

modemmanager: add config optional netifd integration

This change introduces an optional configuration
of the  netifd integration in the ModemManager package.
When disabled, it removes the NETIFD dependency and
other unwanted components from the root filesystem
during the build phase.

Additionally, in the modemmanager.common the netifd-proto.sh
inclusion line can be savely removed as there is no usage
of it in its functions.

Signed-off-by: Gilles Lenaerts <gilles.lenaerts_ext@softathome.com>