Since the ethers(3) functions need to #include <netinet/if_ether.h> to
get:

/* 
 * Ethernet address - 6 octets
 * this is only used by the ethers(3) functions. 
 */   
struct ether_addr {
	u_int8_t ether_addr_octet[6]; 
};    

...why not add the prototypes to the bottom of that file:

#ifndef _KERNEL
#include <sys/cdefs.h>
__BEGIN_DECLS
[ . . . ]
__END_DECLS
#endif /* ! _KERNEL */

Does this sound reasonable?

Jason R. Thorpe                                       thorpej@nas.nasa.gov
NASA Ames Research Center                               Home: 408.866.1912
NAS: M/S 258-6                                          Work: 415.604.0935
Moffett Field, CA 94035                                Pager: 415.428.6939