Move kMaxSegmentSize to constant file (net/)

When building using Jumbo unnamed namespaces gets merged
and variables with the same name conflict. This happens
for the variables kMaxSegmentsSize in:
net/third_party/quic/core/congestion_control/bbr_sender.cc
net/third_party/quic/core/congestion_control/prr_sender.cc

This commit solves the issue by moving the constant to
net/third_party/quic/core/quic_constants.h.

Bug: 772146
Change-Id: I07da21c2bc8c96f6ed5cc83e2724ae948d80a9be
Reviewed-on: https://chromium-review.googlesource.com/1119689
Commit-Queue: Ryan Hamilton <rch@chromium.org>
Reviewed-by: Ryan Hamilton <rch@chromium.org>
Cr-Commit-Position: refs/heads/master@{#571814}
3 files changed