fusefs: Fix a bug during VOP_STRATEGY when the server changes file size
If the FUSE server tells the kernel that a file's size has changed, then
the kernel must invalidate any portion of that file in cache. But the
kernel can't do that during VOP_STRATEGY, because the file's buffers are
already locked. Instead, proceed with the write.
(cherry picked from commit 032a5bd55b3a003d3560435422a95f27f91685fe)