net: initial AF_XDP skeleton

Buildable skeleton of AF_XDP without any functionality. Just what it
takes to register a new address family.

Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 4cafe6a..5c508d2 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -1471,7 +1471,9 @@ static inline u16 socket_type_to_security_class(int family, int type, int protoc
 			return SECCLASS_QIPCRTR_SOCKET;
 		case PF_SMC:
 			return SECCLASS_SMC_SOCKET;
-#if PF_MAX > 44
+		case PF_XDP:
+			return SECCLASS_XDP_SOCKET;
+#if PF_MAX > 45
 #error New address family defined, please update this function.
 #endif
 		}