Add more owners to p2p/OWNERS

I noticed that both owners of this directory were no longer working
on webrtc, so I thought we should add some more owners.

Bug: none
Change-Id: I4975757aee6d7b51980e360b8420366805387002
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1983178
Commit-Queue: Harald Alvestrand <hta@chromium.org>
Reviewed-by: Harald Alvestrand <hta@chromium.org>
Reviewed-by: Sergey Ulanov <sergeyu@chromium.org>
Reviewed-by: Steve Anton <steveanton@chromium.org>
Cr-Commit-Position: refs/heads/master@{#732705}

third_party/blink/renderer/platform/p2p/OWNERS

+guidou@chromium.org
 sergeyu@chromium.org
-juberti@chromium.org
+steveanton@chromium.org
 
 # COMPONENT: Blink>WebRTC