Use state_share_anonymous_io_start for anonymous I/O conflicts with shares

There are several sources of anonymous I/O (basically any I/O not associated
with an NFS v4 stateid). Note that SETATTR of size is considered write I/O.

Any I/O with an NFS v4 special stateid.

Any NFS v3 I/O.

The all-ones NFS v4 special stateid allows READ operations to bypass share deny
read. This patch grants this to NFS v3 READs also.

Note that since NFS v3 offers share reservations via NLM_SHARE, but there is
nothing like a stateid to tie the I/O to the share reservation, we must be
generous and only enforce NFS v4 share deny modes against NFS v3 I/O.

This generosity may be trimmed in the future if NFS v3 I/O is tied to an
NLM_SHARE (for example, we could assume that any I/O coming from the same
host as an applicable NLM_SHARE is using the share, otherwise, we could
conclude such I/O should conflict with any share deny modes.

Signed-off-by: Frank S. Filz <ffilzlnx@mindspring.com>