ANDROID: fuse-bpf: Fix readdir for getdents

If you call getdents with a buffer size less than a page,
entries can be skipped. This correctly sets the point to continue from.

Bug: 325550828
Test: getdents with low buffer size
Signed-off-by: Daniel Rosenberg <drosen@google.com>
(cherry picked from https://android-review.googlesource.com/q/commit:506cf3f0742432c1995117f83b2528a23944989b)
Merged-In: I324e7e815d31742bd4e2d70c5d07c2b09a67a7c2
Change-Id: I324e7e815d31742bd4e2d70c5d07c2b09a67a7c2