Simplify includes in p2ptransportchannel.cc
Simplify includes in p2ptransportchannel.cc

This makes it clearer which code actually depends on the RelayPort
class.

Bug: None
Change-Id: I7b88de1824d5b5832d2f35a8820c5c59d05441c2
Reviewed-on: https://webrtc-review.googlesource.com/100801
Reviewed-by: Qingsi Wang <1c4f50fe02fab79f81be17f4e2f574c199f33efd@webrtc.org>
Commit-Queue: Niels Moller <0057859e47d61d90529d0f66d9ef692cefedb46a@webrtc.org>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#24768}
TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc