Don't flap VCs when carrier state changes; higher-level protocols
can detect loss of connectivity and act accordingly. This is more
consistent with how other network interfaces work.

We no longer use release_vccs() so we can delete it.

release_vccs() was duplicated from net/atm/common.c; make the
corresponding function exported, since other code duplicates it
and could leverage it if it were public.
Signed-off-by: Philip A. Prindeville <philipp@redfish-solutions.com>
Signed-off-by: David S. Miller <davem@davemloft.net>