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.

PR: 256937
Reported by: Agata <chogata@moosefs.pro>
Tested by: Agata <chogata@moosefs.pro>
MFC after: 2 weeks
Reviewed by: pfg
Differential Revision: https://reviews.freebsd.org/D32332