cxgbe/iw_cxgbe: Replace the fatal error flag with a stopped flag.

Now that suspend/resume is supported by the base driver, a fatal error
isn't the only reason that the RNIC can stop abruptly. Also, this state
is no longer permanent as it's possible to resume operations after a
stop. Rename the flag and associated routines to match the new state of
affairs.

MFC after: 1 week
Sponsored by: Chelsio Communications