KEYS: Remove key_type::match in favour of overriding default by match_preparse

A previous patch added a ->match_preparse() method to the key type.  This is
allowed to override the function called by the iteration algorithm.
Therefore, we can just set a default that simply checks for an exact match of
the key description with the original criterion data and allow match_preparse
to override it as needed.

The key_type::match op is then redundant and can be removed, as can the
user_match() function.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
static bool nfs_fattr_map_group_name(struct nfs_server *server, struct nfs_fattr *fattr)
{
	struct nfs4_string *group = fattr->group_name;
	kgid_t gid;

	if (!(fattr->valid & NFS_ATTR_FATTR_GROUP_NAME))
		return false;
	if (nfs_map_group_to_gid(server, group->data, group->len, &gid) == 0) {
		fattr->gid = gid;
		fattr->valid |= NFS_ATTR_FATTR_GROUP;
	}
	return true;
}

static bool nfs_fattr_map_group_name(struct nfs_server *server, struct nfs_fattr *fattr)
{
	struct nfs4_string *group = fattr->group_name;
	kgid_t gid;

	if (!(fattr->valid & NFS_ATTR_FATTR_GROUP_NAME))
		return false;
	if (nfs_map_group_to_gid(server, group->data, group->len, &gid) == 0) {
		fattr->gid = gid;
		fattr->valid |= NFS_ATTR_FATTR_GROUP;
	}
	return true;
}
