net: activity_stats: Add statistics for network transmission activity

When enabled, tracks the frequency of network transmissions
(inbound and outbound) and buckets them accordingly.
Buckets are determined by time between network activity.

Each bucket represents the number of network transmisions that were
N sec or longer apart. Where N is defined as 1 << bucket index.

This network pattern tracking is particularly useful for wireless
networks (ie: 3G) where batching network activity closely together
is more power efficient than far apart.

New file: /proc/net/stat/activity

output:

Min Bucket(sec) Count
              1 7
              2 0
              4 1
              8 0
             16 0
             32 2
             64 1
            128 0

Change-Id: I4c4cd8627b872a55f326b1715c51bc3bdd6e8d92
Signed-off-by: Mike Chan <mike@android.com>
diff --git a/net/Kconfig b/net/Kconfig
index 6ab695a..e569181 100644
--- a/net/Kconfig
+++ b/net/Kconfig
@@ -85,6 +85,14 @@
 	help
 		none
 
+config NET_ACTIVITY_STATS
+	bool "Network activity statistics tracking"
+	default y
+	help
+	 Network activity statistics are useful for tracking wireless
+	 modem activity on 2G, 3G, 4G wireless networks. Counts number of
+	 transmissions and groups them in specified time buckets.
+
 config NETWORK_SECMARK
 	bool "Security Marking"
 	help