netmap: Release lock to avoid deadlock

Issue: 6755

When NetmapOpen encounters an error opening the netmap device, it'll
retry a bit. When the retry limit is reached, it'll shutdown Suricata.

This commit ensures that the device list lock is not held when before
closing all open devices before terminating Suricata.

src/source-netmap.c

@@ -453,6 +453,7 @@ retry:
             }
         }
 
+        SCMutexUnlock(&netmap_devlist_lock);
         NetmapCloseAll();
         FatalError("opening devname %s failed: %s", devname, strerror(errno));
     }