Kernel: Bring up enough networking code that we can respond to ARP requests.

This is all pretty rickety but we can now respond to "arping" from the host
while running inside QEMU. Very cool. :^)

Kernel/StdLib.h

@@ -16,4 +16,7 @@ char *strdup(const char*);
 int memcmp(const void*, const void*, size_t);
 char* strrchr(const char* str, int ch);
 
+inline word ntohs(word w) { return (w & 0xff) << 8 | ((w >> 8) & 0xff); }
+inline word htons(word w) { return (w & 0xff) << 8 | ((w >> 8) & 0xff); }
+
 }