net: Move prototype declaration to header file include/net/dn.h from net/decnet/af_decnet.c

Move prototype declaration of functions to header file include/net/dn.h
from net/decnet/af_decnet.c because they are used by more than one file.

This eliminates the following warning in net/decnet/af_decnet.c:
net/decnet/sysctl_net_decnet.c:354:6: warning: no previous prototype for ‘dn_register_sysctl’ [-Wmissing-prototypes]
net/decnet/sysctl_net_decnet.c:359:6: warning: no previous prototype for ‘dn_unregister_sysctl’ [-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/dn.h

···
 }
 
 unsigned int dn_mss_from_pmtu(struct net_device *dev, int mtu);
+void dn_register_sysctl(void);
+void dn_unregister_sysctl(void);
 
 #define DN_MENUVER_ACC 0x01
 #define DN_MENUVER_USR 0x02

net/decnet/af_decnet.c

···
 	.sendpage =	sock_no_sendpage,
 };
 
-void dn_register_sysctl(void);
-void dn_unregister_sysctl(void);
-
 MODULE_DESCRIPTION("The Linux DECnet Network Protocol");
 MODULE_AUTHOR("Linux DECnet Project Team");
 MODULE_LICENSE("GPL");