libbinder: send is non-blocking and interruptible

We actually don't use MSG_DONTBLOCK now, but we only read after
receiving POLLOUT. However, by polling, send also now plugs into the
shutdown triggers. As a side effect, this causes send calls to fail
earlier.

Bug: 186470974
Test: binderRpcTest
Change-Id: Ia13d0dc1749fa7c10340e07e221b4b682cc59cc8