@rfjakob reports that after bdca0e6a (Add support for store notify)
build got broken on ARM:

	$ GOARCH=arm go build ./example/loopback
	# github.com/hanwen/go-fuse/fuse
	fuse/server.go:490:11: constant 4294967295 overflows int
	fuse/server.go:492:9: constant 4294967295 overflows int

Fix it by amending "store notify" patch by chunking data into 2GB instead of
full-32bit-range 4GB.