RT correction in DV

[leonardomaccari]

A small fix to the RT of router B in the DV description.

[qdeconinck]

This PR also includes PR #131. Please remove the changes from #131 or close #131 instead, otherwise this may later introduce conflicts.

[leonardomaccari]

sorry, I pushed to master :-(
I closed #131

[qdeconinck]

Not strong opinion about this PR. This sounds ok to me, though having sub-bullets (e.g., 2.a and 2.b) may be clearer in my opinion.

Also, it would be nice if the first commit message describes the performed changes (instead of "Update network.rst")

[qdeconinck]

Suggested change

	Consider in the network above that host `A` wants to send a 900 bytes packet (870 bytes of payload and 30 bytes of header) to host `B` via router `R1`. Host `A` encapsulates this packet inside a single frame. The frame is received by router `R1` which extracts the packet. Router `R1` has three possible options to process this packet:
	Consider in the network above that host `A` wants to send a 900 bytes packet (870 bytes of payload and 30 bytes of header) to host `B` via router `R1`. Host `A` encapsulates this packet inside a single frame. The frame is received by router `R1` which extracts the packet. Router `R1` has three possible options to process this packet.