Make all std::regex instances static

Per [1] we really shouldn't be using regex.  In the cases we do, it's a
HUUUUUGE performance benefit to be compiling the regex ONCE.

The only downside is a slight increase in memory usage.

[1]: https://github.com/openbmc/bmcweb/issues/176

Signed-off-by: Ed Tanous <edtanous@google.com>
Change-Id: I8644b8a07810349fb60bfa0258a13e815912a38e
diff --git a/include/dbus_monitor.hpp b/include/dbus_monitor.hpp
index 46ef25e..4ecc436 100644
--- a/include/dbus_monitor.hpp
+++ b/include/dbus_monitor.hpp
@@ -173,8 +173,8 @@
 
         // These regexes derived on the rules here:
         // https://dbus.freedesktop.org/doc/dbus-specification.html#message-protocol-names
-        std::regex validPath("^/([A-Za-z0-9_]+/?)*$");
-        std::regex validInterface(
+        static std::regex validPath("^/([A-Za-z0-9_]+/?)*$");
+        static std::regex validInterface(
             "^[A-Za-z_][A-Za-z0-9_]*(\\.[A-Za-z_][A-Za-z0-9_]*)+$");
 
         for (const auto& thisPath : *paths)