Revert "tcp: reduce POLLOUT events caused by TCP_NOTSENT_LOWAT"

This reverts commit 0d70e638.  It is
part of a series that breaks the kernel abi for Android.  For this
kernel tree, we do not care so much about KASAN, so it's not a big issue
to revert.  If it is needed in the future, it can be brought back in an
abi-safe way.

Bug: 161946584
Change-Id: Ie4c15028abda17a6ea6e023fb046c7b2e3ca6827
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>