net: udp4: move GSO functions to udp_offload

Similarly to TCP offloading and UDPv6 offloading, move all related
UDPv4 functions to udp_offload.c to make things more explicit. Also,
by this, we can make those functions static.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/udp.h b/include/net/udp.h
index 065f379..b30a71a 100644
--- a/include/net/udp.h
+++ b/include/net/udp.h
@@ -187,6 +187,8 @@
 extern int udp_disconnect(struct sock *sk, int flags);
 extern unsigned int udp_poll(struct file *file, struct socket *sock,
 			     poll_table *wait);
+extern struct sk_buff *skb_udp_tunnel_segment(struct sk_buff *skb,
+					      netdev_features_t features);
 extern int udp_lib_getsockopt(struct sock *sk, int level, int optname,
 			      char __user *optval, int __user *optlen);
 extern int udp_lib_setsockopt(struct sock *sk, int level, int optname,
@@ -262,11 +264,10 @@
 extern void udp4_proc_exit(void);
 #endif
 
+extern int udpv4_offload_init(void);
+
 extern void udp_init(void);
 
-extern int udp4_ufo_send_check(struct sk_buff *skb);
-extern struct sk_buff *udp4_ufo_fragment(struct sk_buff *skb,
-	netdev_features_t features);
 extern void udp_encap_enable(void);
 #if IS_ENABLED(CONFIG_IPV6)
 extern void udpv6_encap_enable(void);