[REQUEST] Also monitor packets per second (PPS) in network panel

[fabianbees]

Is your feature request related to a problem? Please describe.
I also need to monitor the Packets per Second (PPS) for each network interface. btop only shows the bandwidth.
Therfore an additional tool, like vnstat, needs to be used, which is very cumbersome when btop can quickly switch between different interfaces and show their stats.

Describe the solution you'd like
Also include the PPS (packets per seconds) metric in the network panel.

This could be implemeted in two ways:

1. Silmpler solution:
   Show current PPS for download/upload above or below the current bandwidth:
   

2. More elegant solution:

• Introduce a new switch in the header of the network panel, next to sync, auto, zero ...
• This switch now toggles the entire network panel (including the graphs) from PPS to bandwith
  The PPS view could look like this: