block: use 'unsigned' for in_flight field on driver state

This patch makes in_flight field 'unsigned' for BDRVNBDState and
MirrorBlockJob. This matches the definition of this field on BDS
and is generically correct - we should never get negative value here.

Signed-off-by: Denis V. Lunev <den@openvz.org>
CC: John Snow <jsnow@redhat.com>
CC: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
CC: Kevin Wolf <kwolf@redhat.com>
CC: Hanna Reitz <hreitz@redhat.com>
CC: Eric Blake <eblake@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>

block/mirror.c

@@ -73,7 +73,7 @@ typedef struct MirrorBlockJob {
 
     uint64_t last_pause_ns;
     unsigned long *in_flight_bitmap;
-    int in_flight;
+    unsigned in_flight;
     int64_t bytes_in_flight;
     QTAILQ_HEAD(, MirrorOp) ops_in_flight;
     int ret;

block/nbd.c

@@ -77,7 +77,7 @@ typedef struct BDRVNBDState {
     QemuMutex requests_lock;
     NBDClientState state;
     CoQueue free_sema;
-    int in_flight;
+    unsigned in_flight;
     NBDClientRequest requests[MAX_NBD_REQUESTS];
     QEMUTimer *reconnect_delay_timer;