ext2fs: passthrough any extra timestamps to the dinode struct.

In general we don't trust any of the extended timestamps unless the
EXT2F_ROCOMPAT_EXTRA_ISIZE feature is set. However, in the case where
we freshly allocated a new inode the information is valid and it is
better to pass it along instead of leaving the value undefined.

This should have no practical effect but should reduce the amount of
garbage if EXT2F_ROCOMPAT_EXTRA_ISIZE is set, like in cases where the
filesystem is converted from ext3 to ext4.

MFC after: 4 days