irmap: Add option that forces fsnotify watches paths resolve

When migrating container with copying its FS, the inode numbers
and thus their handles wil change. This will make the restore of
inotify/fanotify fail, since they do it via fhandles.

We've already faced the problems with fsnotifies on NFS -- they
don't work there. To address this an irmap cache is created on
pre-dump, so to resolve the issue with changed inodes during
migration, we can force the irmap cache build.

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
irmap: Properly compare stat vs proc devices

The s_dev value we see in irmap is get from proc file and is
raw kernel dev_t. We compare this value to the device get from
stat syscall, which is old-style dev_t (with less bits for minor).

Thus, need to convert kernel dev_t to stat's dev_t for proper
comparison.

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>