Use more C++17 features

Mainly structured bindings, inline variables, and class template
argument deduction, plus many more smaller things.

Change-Id: I810d17e0adb470426e4e30c898e03b3140ad052f
diff --git a/core/network.cpp b/core/network.cpp
index eafc388..bfecec5 100644
--- a/core/network.cpp
+++ b/core/network.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2018,  Regents of the University of California,
+ * Copyright (c) 2014-2022,  Regents of the University of California,
  *                           Arizona Board of Regents,
  *                           Colorado State University,
  *                           University Pierre & Marie Curie, Sorbonne University,
@@ -59,7 +59,7 @@
 }
 
 bool
-Network::isValidCidr(const std::string& cidr)
+Network::isValidCidr(std::string_view cidr)
 {
   auto pos = cidr.find('/');
   if (pos == std::string::npos) {