[SCSI] iscsi_tcp: fix relogin/shutdown hang

[SCSI] iscsi_tcp: fix relogin/shutdown hang

When I made this patch:
b64e77f70b8c11766e967e3485331a9e6ef01390
it was to solve a problem where we were already on the waitqueue
becuase a connection problem/logout caused us to be on there
when we were cleaning up the session. If we happen to get
on queue for more normal reasons like their just does not happen
to be any send space at the same time we are closing the connection
we hit a race and get stuck in the wait.

We should not check if the waitqueue is active
because we could race with the network code. If
the network xmit code is just about to enter the
prepare to wait when we check for the waitqueue to
be active then we will miss each other and the
network code will fall into the wait and we will
not run wake_up.

Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>