Add bengr to OWNERS for socket_performance_watcher*
Add bengr to OWNERS for socket_performance_watcher*

net/base/socket_performance_watcher* files are used only
for/by NQE related code. By adding bengr@ to OWNERS, it
reduces the trouble of asking net/ reviewers to review that
file.

e.g., in https://codereview.chromium.org/1672513002/,
net/ reviewers only need to look at net/quic/* files.

BUG=
NOTRY=true

Review URL: https://codereview.chromium.org/1743843002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#378246}

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