cifs: failure to add channel on iface should bump up weight

[ Upstream commit 6aac002b ]

After the interface selection policy change to do a weighted
round robin, each iface maintains a weight_fulfilled. When the
weight_fulfilled reaches the total weight for the iface, we know
that the weights can be reset and ifaces can be allocated from
scratch again.

During channel allocation failures on a particular channel,
weight_fulfilled is not incremented. If a few interfaces are
inactive, we could end up in a situation where the active
interfaces are all allocated for the total_weight, and inactive
ones are all that remain. This can cause a situation where
no more channels can be allocated further.

This change fixes it by increasing weight_fulfilled, even when
channel allocation failure happens. This could mean that if
there are temporary failures in channel allocation, the iface
weights may not strictly be adhered to. But that's still okay.

Fixes: a6d8fb54 ("cifs: distribute channels across interfaces based on speed")
Signed-off-by: Shyam Prasad N <sprasad@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>