Revert "tcp: return EPOLLOUT from tcp_poll only when notsent_bytes is half the limit"

This reverts commit 7e120db7.  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: I2bb3f5516eef5546fd2fa8dc5621f82d22847b7f
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>