blkdebug: protect rules and suspended_reqs with a lock

blkdebug: protect rules and suspended_reqs with a lock

First, categorize the structure fields to identify what needs
to be protected and what doesn't.

We essentially need to protect only .state, and the 3 lists in
BDRVBlkdebugState.

Then, add the lock and mark the functions accordingly.

Co-developed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Message-Id: <20210614082931.24925-7-eesposit@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>