stp.h: Remove extern from function prototypes

There are a mix of function prototypes with and without extern
in the kernel sources.  Standardize on not using extern for
function prototypes.

Function prototypes don't need to be written with extern.
extern is assumed by the compiler.  Its use is as unnecessary as
using auto to declare automatic/local variables in a block.
Signed-off-by: NJoe Perches <joe@perches.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/net/stp.h

@@ -8,7 +8,7 @@ struct stp_proto {
 	void		*data;
 };
 
-extern int stp_proto_register(const struct stp_proto *proto);
-extern void stp_proto_unregister(const struct stp_proto *proto);
+int stp_proto_register(const struct stp_proto *proto);
+void stp_proto_unregister(const struct stp_proto *proto);
 
 #endif /* _NET_STP_H */