use restrict everywhere it's required by c99 and/or posix 2008

to deal with the fact that the public headers may be used with pre-c99
compilers, __restrict is used in place of restrict, and defined
appropriately for any supported compiler. we also avoid the form
[restrict] since older versions of gcc rejected it due to a bug in the
original c99 standard, and instead use the form *restrict.

src/network/accept.c

@@ -2,7 +2,7 @@
 #include "syscall.h"
 #include "libc.h"
 
-int accept(int fd, struct sockaddr *addr, socklen_t *len)
+int accept(int fd, struct sockaddr *restrict addr, socklen_t *restrict len)
 {
 	return socketcall_cp(accept, fd, addr, len, 0, 0, 0);
 }