move src/syscall to src/lib/syscall.

enforce rule: all kernel data structures and constants
	go in syscall module.
move things that should be in syscall out of net.
make net a single package.

R=r
OCL=15985
CL=15994

src/lib/net/ip.go

@@ -10,7 +10,7 @@
 // This library accepts either size of byte array but always
 // returns 16-byte addresses.
 
-package ip
+package net
 
 export const (
 	IPv4len = 4;