pybootchartgui: visualize /proc/net/dev network stats in graphs

This patch adds support for parsing and visualizing network interface statistics from /proc/net/dev in pybootchartgui. It introduces a new NetSample class to hold per-interface metrics, including received/transmitted bytes and their deltas over time.

The data is drawn using line and box charts in draw.py and helps to monitor
network usage during the boot process for each interface individually.

(From OE-Core rev: 9e640022c83a627bd05c23b66b658bd644b2f0d7)

Signed-off-by: denisova-ok <denisova.olga.k@yandex.ru>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/pybootchartgui/pybootchartgui/samples.py

@@ -37,6 +37,16 @@ class CPUSample:
         return str(self.time) + "\t" + str(self.user) + "\t" + \
                str(self.sys) + "\t" + str(self.io) + "\t" + str (self.swap)
 
+
+class NetSample:
+    def __init__(self, time, iface, received_bytes, transmitted_bytes, receive_diff, transmit_diff):
+        self.time = time
+        self.iface = iface
+        self.received_bytes = received_bytes
+        self.transmitted_bytes = transmitted_bytes
+        self.receive_diff = receive_diff
+        self.transmit_diff = transmit_diff
+
 class CPUPressureSample:
     def __init__(self, time, avg10, avg60, avg300, deltaTotal):
         self.time = time