tcp: add a sysctl to config the tcp_default_init_rwnd

The default initial rwnd was hardcoded to 10.

Now we allow it to be controlled via
  /proc/sys/net/ipv4/tcp_default_init_rwnd
which limits the values from 3 to 100

This is somewhat needed because ipv6 routes are
autoconfigured by the kernel.

See "An Argument for Increasing TCP's Initial Congestion Window"
in https://developers.google.com/speed/articles/tcp_initcwnd_paper.pdf

Change-Id: I7eac8a0a5133371aea9ecb9aec0b608bd7f2cc57
Signed-off-by: JP Abgrall <jpa@google.com>
Signed-off-by: zwliew <zhaoweiliew@gmail.com>
android: configs: Grab the android/configs from kernel/common

This is a squash of all changes from kernel/common android-3.4 up to
  5e35d66 android: configs: add IPV6 ROUTE INFO

Change-Id: I848f1865ec7da1dfc3338a3e9d7f944a6f00f2a6
Signed-off-by: JP Abgrall <jpa@google.com>
Signed-off-by: zwliew <zhaoweiliew@gmail.com>
android: configs: Add CONFIG_NETFILTER_XT_TARGET_IDLETIMER

Signed-off-by: Ashish Sharma <ashishsharma@google.com>
Signed-off-by: zwliew <zhaoweiliew@gmail.com>
android: base-cfg: enable DM_VERITY (used for secureboot)

Change-Id: I68d769f97ffa76bb45e65d34a96dd7f558c02d08
Signed-off-by: JP Abgrall <jpa@google.com>
(cherry picked from commit 37cb5bec8983e505eecb730188bfc113d087dee7)
Signed-off-by: zwliew <zhaoweiliew@gmail.com>
Makefile: build with -pipe flag

This flag uses pipes instead of temporary files for communication between the various stages of compilation. Thus, it preserves the lifetime of SSDs due to fewer R/W operations.

Signed-off-by: zwliew <zhaoweiliew@gmail.com>