o linux/net.h: prune the include dependency tree, remove include socket.h

Use struct forward declaration and fix irda.h and netlink.h to include what
uses (only sa_family_t).

include/linux/irda.h

@@ -25,6 +25,8 @@
 #ifndef KERNEL_IRDA_H
 #define KERNEL_IRDA_H
 
+#include <linux/socket.h> /* only for sa_family_t */
+
 /* Hint bit positions for first hint byte */
 #define HINT_PNP         0x01
 #define HINT_PDA         0x02

include/linux/net.h

@@ -19,7 +19,6 @@
 #define _LINUX_NET_H
 
 #include <linux/config.h>
-#include <linux/socket.h>
 #include <linux/wait.h>
 
 struct poll_table_struct;
@@ -88,6 +87,8 @@ struct socket {
 struct vm_area_struct;
 struct page;
 struct kiocb;
+struct sockaddr;
+struct msghdr;
 
 struct proto_ops {
 	int		family;
@@ -136,6 +137,8 @@ struct net_proto_family {
 	short	encrypt_net;
 };
 
+struct iovec;
+
 extern int	     sock_wake_async(struct socket *sk, int how, int band);
 extern int	     sock_register(struct net_proto_family *fam);
 extern int	     sock_unregister(int family);

include/linux/netlink.h

 #ifndef __LINUX_NETLINK_H
 #define __LINUX_NETLINK_H
 
+#include <linux/socket.h> /* for sa_family_t */
+
 #define NETLINK_ROUTE		0	/* Routing/device hook				*/
 #define NETLINK_SKIP		1	/* Reserved for ENskip  			*/
 #define NETLINK_USERSOCK	2	/* Reserved for user mode socket protocols 	*/