gigaset: accept connection establishment messages in any order

ISDN connection setup failed if the "connection active" and
"B channel up" messages from the device arrived in a different
order than expected. Modify the state machine to accept them in
any order.

Impact: bugfix
Signed-off-by: Tilman Schmidt <tilman@imap.cc>
CC: stable <stable@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>