Add buffer size to Link, defaults to infinite buffer.
Add sequence number field to Packet
Make Rat immune to losses.
Assume all pkts are delivered while reset()ing to prevent deadlocks.
Change interface to packets_received()
Aimd with slow start, will test now.
1. Reduce cwnd at most once per RTT per RFC 4341.
2. Don't let cwnd drop below 1.
3. Don't invoke congestion control for packets from old flows.
Assume all AIMD pkts are delivered while reset()ing to prevent deadlocks.
network.hh: Have setters return reference in case need to mutate existing obj
rat: Allow cap on flow size

Conflicts:
	src/rat-templates.cc
sendergang: Split SwitchedSender into Time/Byte SwitchedSender

Conflicts:
	src/sendergang.cc
sendergang: Separate out methods for SwitchedSender vs. derived classes
sendergang: More OOP cleanup
sendergang: Add ByteSwitchedSender implementation

Conflicts:
	src/sendergang.cc
ByteSwitchSender must turn off as soon as it sends the required packets.
sendergang.cc: Make sure flow length is > 0
Wonder how this compiled: returns ref to a local variable
Fix build errors after rebase
Eliminate SenderGang::senders method
sendergang: Split out switching step into new method