treewide: Make logging variables more consistent

This aims to better group related variables and differentiate keywords
like INTERFACE_NAME into NET vs DBUS.

Tested: Ran on a machine to verify that our info log messages still look
sane in the journal.

Change-Id: Ic4d1faaaf5c432e69cacd387fa972481916b6bc8
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/src/dhcp_configuration.cpp b/src/dhcp_configuration.cpp
index 8843c7c..c649568 100644
--- a/src/dhcp_configuration.cpp
+++ b/src/dhcp_configuration.cpp
@@ -44,7 +44,7 @@
     }
     if (newest_file != std::filesystem::directory_entry{})
     {
-        lg2::info("Using DHCP options from {FILE}", "FILE",
+        lg2::info("Using DHCP options from {CFG_FILE}", "CFG_FILE",
                   newest_file.path().native());
         conf.setFile(newest_file.path());
     }