Add clang-format file

Also run it across the whole tree to get everything using the One True Style.
We don't yet run this in an automated fashion as it's a little slow, but
there is a snippet to do so in makeall.sh.

Kernel/Net/EtherType.h

@@ -3,8 +3,9 @@
 #include <AK/Types.h>
 
 struct EtherType {
-enum : word {
-    ARP = 0x0806,
-    IPv4 = 0x0800,
-};
+    enum : word
+    {
+        ARP = 0x0806,
+        IPv4 = 0x0800,
+    };
 };