CAPI: Issue synchronous hangup on capincci_free_minor

capincci_free and, thus, capincci_free_minor runs in process context, so
we can issue the hangup of the associated TTY synchronously.

Signed-off-by: Jan Kiszka <jan.kiszka@web.de>
Signed-off-by: David S. Miller <davem@davemloft.net>