unix: implement Linux AF_XDP sockets

Provides access to the Linux AF_XDP socket family.  For more
information on AF_XDP, see:
https://www.kernel.org/doc/html/latest/networking/af_xdp.html.

Change-Id: I7efb82c4a67da3e15932e3c0d882f0bad7ba16ef
Reviewed-on: https://go-review.googlesource.com/136695
Run-TryBot: Matt Layher <mdlayher@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>

unix/linux/types.go

@@ -75,6 +75,7 @@ package unix
 #include <linux/rtc.h>
 #include <linux/blkpg.h>
 #include <linux/net_namespace.h>
+#include <linux/if_xdp.h>
 
 // abi/abi.h generated by mkall.go.
 #include "abi/abi.h"
@@ -427,6 +428,8 @@ type RawSockaddrALG C.struct_sockaddr_alg
 
 type RawSockaddrVM C.struct_sockaddr_vm
 
+type RawSockaddrXDP C.struct_sockaddr_xdp
+
 type RawSockaddr C.struct_sockaddr
 
 type RawSockaddrAny C.struct_sockaddr_any
@@ -474,6 +477,7 @@ const (
 	SizeofSockaddrCAN       = C.sizeof_struct_sockaddr_can
 	SizeofSockaddrALG       = C.sizeof_struct_sockaddr_alg
 	SizeofSockaddrVM        = C.sizeof_struct_sockaddr_vm
+	SizeofSockaddrXDP       = C.sizeof_struct_sockaddr_xdp
 	SizeofLinger            = C.sizeof_struct_linger
 	SizeofIovec             = C.sizeof_struct_iovec
 	SizeofIPMreq            = C.sizeof_struct_ip_mreq
@@ -1565,3 +1569,15 @@ const (
 	NETNSA_PID  = C.NETNSA_PID
 	NETNSA_FD   = C.NETNSA_FD
 )
+
+// AF_XDP:
+
+type XDPRingOffset C.struct_xdp_ring_offset
+
+type XDPMmapOffsets C.struct_xdp_mmap_offsets
+
+type XDPUmemReg C.struct_xdp_umem_reg
+
+type XDPStatistics C.struct_xdp_statistics
+
+type XDPDesc C.struct_xdp_desc