net: ipv4: Remove extern udp_v4_early_demux()/tcp_v4_early_demux() in .c files

Function udp_v4_early_demux() was already declared in 'include/net/udp.h',
no need to keep the extern in 'ip_input.c', which may produce the
following checkpatch warning:

WARNING: externs should be avoided in .c files
#45: FILE: net/ipv4/ip_input.c:322:
+enum skb_drop_reason udp_v4_early_demux(struct sk_buff *skb);

Replace it by including 'net/udp.h'. Do the same for tcp_v4_early_demux().

Signed-off-by: Wang Liang <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

net/ipv4/ip_input.c

···
 #include <linux/mroute.h>
 #include <linux/netlink.h>
 #include <net/dst_metadata.h>
+#include <net/udp.h>
+#include <net/tcp.h>
 
 /*
  *	Process Router Attention IP option (RFC 2113)
···
 	       ip_hdr(hint)->tos == iph->tos;
 }
 
-int tcp_v4_early_demux(struct sk_buff *skb);
-enum skb_drop_reason udp_v4_early_demux(struct sk_buff *skb);
 static int ip_rcv_finish_core(struct net *net,
 			      struct sk_buff *skb, struct net_device *dev,
 			      const struct sk_buff *hint)