fuse: document protocol version negotiation
fuse: document protocol version negotiation

Clarify how the protocol version should be negotiated between kernel
and userspace.  Notably libfuse didn't correctly handle the case when
the supported major versions didn't match.

Signed-off-by: Miklos Szeredi <84cd5483a2f9acd1c37251cba7c2908448f221b8@suse.cz>

TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas