AK: Rename the common integer typedefs to make it obvious what they are.

These types can be picked up by including <AK/Types.h>:

* u8, u16, u32, u64 (unsigned)
* i8, i16, i32, i64 (signed)

Kernel/Net/EtherType.h

@@ -3,7 +3,7 @@
 #include <AK/Types.h>
 
 struct EtherType {
-    enum : word {
+    enum : u16 {
         ARP = 0x0806,
         IPv4 = 0x0800,
     };