cifs: cifs_pick_channel should try selecting active channels

cifs_pick_channel today just selects a channel based
on the policy of least loaded channel. However, it
does not take into account if the channel needs
reconnect. As a result, we can have failures in send
that can be completely avoided.

This change doesn't make a channel a candidate for
this selection if it needs reconnect.

Signed-off-by: Shyam Prasad N <sprasad@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>