dahdi: Move clearing of DAHDI_ALARM_NOTOPEN to __dahdi_assign_span().

Previously this was in __dahdi_init_span(). The problem was that
__dahdi_init_span() was only called when a spans' line mode was being changed.
Therefore it was possible to unassign and resassign an analog span and leave it
stuck in the 'NOP' alarm state.

It also make the setting / clearing of DAHDI_ALARM_NOTOPEN symetrical about span
unassignment / assignment in addition to updating the alarm states on all the
channels on the span via the dahdi_alarm_notify() function.

This is a better version of commit 496f81777323d309bd5c32afc2186bdc0055e5be.

Signed-off-by: Shaun Ruffell <sruffell@digium.com>
dahdi: Change auto_assign_spans default from 1 to 0.

The infrastructure has been put in place in 2.8.0 for fully dynamic device and
span configuration. This will be the default mode in DAHDI-Linux 2.9.0.

Signed-off-by: Shaun Ruffell <sruffell@digium.com>
Acked-by: Tzafrir Cohen <tzafrir.cohen@xorcom.com>
Acked-by: Russ Meyerriecks <rmeyerriecks@digium.com>
Acked-by: Oron Peled <oron.peled@xorcom.com>