Ruby: Improve Change PerfectSwitch's wakeup function

Ruby: Improve Change PerfectSwitch's wakeup function
Currently the wakeup function for the PerfectSwitch contains three loops -

loop on number of virtual networks
  loop on number of incoming links
	    loop till all messages for this (link, network) have been routed

With an 8 processor mesh network and Hammer protocol, about 11-12% of the
was observed to have been spent in this function, which is the highest
amongst all the functions. It was found that the innermost loop is executed
about 45 times per invocation of the wakeup function, when each invocation
of the wakeup function processes just about one message.

The patch tries to do away with the redundant executions of the innermost
loop. Counters have been added for each virtual network that record the
number of messages that need to be routed for that virtual network. The
inner loops are only executed when the number of messages for that particular
virtual network > 0. This does away with almost 80% of the executions of the
innermost loop. The function now consumes about 5-6% of the total execution
time.