smb/client: refresh allocation after EOF-extending fallocate

smb/client: refresh allocation after EOF-extending fallocate

Before this change, xfstests generic/496 was not supported on ksmbd:

        generic/496 ... [not run] fallocated swap not supported here

ksmbd handles SetEOF as truncate, so EOF extension alone does not
allocate backing blocks. A fallocated swapfile can therefore still
look sparse to swapon.

Request allocation for EOF-extending fallocate ranges that can be
represented by FILE_ALLOCATION_INFORMATION, and refresh the allocation
state afterwards.

With this change, xfstests generic/496 and generic/701 pass on ksmbd.

However, Samba "strict allocate = no" now exposes the real generic/701
failure: the old pass came from inflated local i_blocks, not from
server allocation. generic/213 also fails in that case because an
oversized allocation request may not return ENOSPC.

Signed-off-by: Huiwen He <hehuiwen@kylinos.cn>
Reviewed-by: ChenXiaoSong <chenxiaosong@kylinos.cn>
Signed-off-by: Steve French <stfrench@microsoft.com>