unix: add sockaddr and defines for PPPoE sockets.

`sockaddr_pppox` is a packed struct, which godefs doesn't understand.
So, I had to do the byte packing by hand instead.

Change-Id: Ib92cf43f8ae0729a0af043c4241063911c95e6bf
GitHub-Last-Rev: 8982dec099594064d3892f3fa05bb7b5989cec6d
GitHub-Pull-Request: golang/sys#23
Reviewed-on: https://go-review.googlesource.com/c/149757
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>

unix/linux/types.go

@@ -48,6 +48,7 @@ package unix
 #include <sys/wait.h>
 #include <linux/filter.h>
 #include <linux/icmpv6.h>
+#include <linux/if_pppox.h>
 #include <linux/keyctl.h>
 #include <linux/netfilter/nf_tables.h>
 #include <linux/netfilter/nfnetlink.h>
@@ -168,6 +169,7 @@ union sockaddr_all {
 	struct sockaddr_un s4;
 	struct sockaddr_ll s5;
 	struct sockaddr_nl s6;
+	struct sockaddr_pppox s7;
 };
 
 struct sockaddr_any {
@@ -432,6 +434,8 @@ type RawSockaddrVM C.struct_sockaddr_vm
 
 type RawSockaddrXDP C.struct_sockaddr_xdp
 
+type RawSockaddrPPPoX [C.sizeof_struct_sockaddr_pppox]byte
+
 type RawSockaddr C.struct_sockaddr
 
 type RawSockaddrAny C.struct_sockaddr_any
@@ -480,6 +484,7 @@ const (
 	SizeofSockaddrALG       = C.sizeof_struct_sockaddr_alg
 	SizeofSockaddrVM        = C.sizeof_struct_sockaddr_vm
 	SizeofSockaddrXDP       = C.sizeof_struct_sockaddr_xdp
+	SizeofSockaddrPPPoX     = C.sizeof_struct_sockaddr_pppox
 	SizeofLinger            = C.sizeof_struct_linger
 	SizeofIovec             = C.sizeof_struct_iovec
 	SizeofIPMreq            = C.sizeof_struct_ip_mreq