ALII-4573 WIP Purge always returns

@raensink @karlj-spindance please review.  

These changes keep lwIP from hanging when it times out TCP/IP connection (a PCB).  We book keep if a task was blocking on PCB and we return an error to
the blocking task when we delete the connection.  Typical reason is that it is sitting idle for 2*MSL which is current 2*4 seconds or 8 seconds.

Signed-off-by: Mike Stitt <mikes@spindance.com>