Reduce AppFuse max read size.

Since the max read size of FUSE is 128KB in default, the socket header
of the appfuse epollcontroller is allocated in order 4 (64KB).  When
memory environment is in insufficient situation that has a lot of
fragment, order 4 size memory allication is impossible, so more than
several tens of seconds could take to allocate the socket header.

To prevent the issue, limit the fuse read size to 64KB, so that the
memory allocation order of the socket header is changed to order 2.

Bug: 312503249
Test: atest AppFusePerfTest
Change-Id: I7020801b7539d980515885396916f8be1f1008e9