net: Move prototype declaration to header file include/net/datalink.h from net/ipx/af_ipx.c

Move prototype declarations of function to header file
include/net/datalink.h from net/ipx/af_ipx.c because they are used by
more than one file.

This eliminates the following warning in net/ipx/pe2.c:
net/ipx/pe2.c:20:24: warning: no previous prototype for ‘make_EII_client’ [-Wmissing-prototypes]
net/ipx/pe2.c:32:6: warning: no previous prototype for ‘destroy_EII_client’ [-Wmissing-prototypes]

Signed-off-by: Rashika Kheria <[e-mail]>
Reviewed-by: Josh Triplett <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/datalink.h

···
 	struct list_head node;
 };
 
+struct datalink_proto *make_EII_client(void);
+void destroy_EII_client(struct datalink_proto *dl);
 #endif

net/ipx/af_ipx.c

···
 #include <net/p8022.h>
 #include <net/psnap.h>
 #include <net/sock.h>
+#include <net/datalink.h>
 #include <net/tcp_states.h>
 
 #include <asm/uaccess.h>
···
 static struct notifier_block ipx_dev_notifier = {
 	.notifier_call	= ipxitf_device_event,
 };
-
-extern struct datalink_proto *make_EII_client(void);
-extern void destroy_EII_client(struct datalink_proto *);
 
 static const unsigned char ipx_8022_type = 0xE0;
 static const unsigned char ipx_snap_id[5] = { 0x0, 0x0, 0x0, 0x81, 0x37 };