pd: On invalid request, send reject and go to SRC_READY
pd: On invalid request, send reject and go to SRC_READY

When a source gets an invalid request, send reject, but still go to
SRC_READY state and keep the old power contract in place.

BUG=chrome-os-partner:34987
BRANCH=samus
TEST=load onto zinger. on samus add custom code to always send an
invalid request. note that zinger still transitions to SRC_READY,
samus still transitions to SNK_READY, data swap is still performed,
discover identity is still performed, and samus still draws 5V/3A.

Change-Id: I1213688f2b205636b3657afb1a4d8f7929bfe7ee
Signed-off-by: Alec Berg <1a4429eeda29095a12e19a73405f80f5b7f37a63@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/238250
Reviewed-by: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>
(cherry picked from commit 1f55eea80994538350588eb27dce0ee791144e2e)
Signed-off-by: Alec Berg <1a4429eeda29095a12e19a73405f80f5b7f37a63@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/238608

thehobn/ec,thehobn/ec,thehobn/ec,thehobn/ec