Add extern "C" defines using BEGIN_DECL for the BSD kernel code.

bsd/sys/net/ethernet.h

@@ -370,6 +370,8 @@ struct ether_addr {
 
 #ifdef _KERNEL
 
+__BEGIN_DECLS
+
 struct ifnet;
 struct mbuf;
 struct route;
@@ -390,6 +392,8 @@ void	ether_vlan_mtap(struct bpf_if *, struct mbuf *,
 	    void *, u_int);
 struct mbuf  *ether_vlanencap(struct mbuf *, uint16_t);
 
+__END_DECLS
+
 #else /* _KERNEL */
 
 #include <sys/cdefs.h>

bsd/sys/net/if_var.h

@@ -36,6 +36,8 @@
 #include <bsd/porting/rwlock.h>
 #include <bsd/sys/net/if.h>
 
+__BEGIN_DECLS
+
 /*
  * Structures defining a network interface, providing a packet
  * transport mechanism (ala level 0 of the PUP protocols).
@@ -830,4 +832,6 @@ void	if_deregister_com_alloc(u_char type);
 
 #endif /* _KERNEL */
 
+__END_DECLS
+
 #endif /* !_NET_IF_VAR_H_ */