smb: client: fix regression with mount options parsing

smb: client: fix regression with mount options parsing

After commit 1ef15fbe6771 ("cifs: client: enforce consistent handling
of multichannel and max_channels"), invalid mount options started to
be ignored, allowing cifs.ko to proceed with the mount instead of
baling out.

The problem was related to smb3_handle_conflicting_options() being
called even when an invalid parameter had been parsed, overwriting the
return value of vfs_parse_fs_string() in
smb3_fs_context_parse_monolithic().

Fix this by calling smb3_handle_conflicting_options() only when a
valid mount option has been passed.

Reproducer:

$ mount.cifs //srv/share /mnt -o ${opts}
$ mount -o remount,foo,${opts} /mnt # must fail

Fixes: 1ef15fbe6771 ("cifs: client: enforce consistent handling of multichannel and max_channels")
Reported-by: Xiaoli Feng <xifeng@redhat.com>
Signed-off-by: Paulo Alcantara (Red Hat) <pc@manguebit.org>
Cc: David Howells <dhowells@redhat.com>
Cc: linux-cifs@vger.kernel.org
Signed-off-by: Steve French <stfrench@microsoft.com>