Use struct in_addr rather than just "in_addr".

Add struct sockaddr_in.

src/include/in.h

 #ifndef	_IN_H
 #define	_IN_H
 
+#include "stdint.h"
 #include <if_ether.h>
 #define IP		ETH_P_IP
 #define ARP		ETH_P_ARP
 /* Same after going through htonl */
 #define IP_BROADCAST	0xFFFFFFFF
 
-typedef struct {
+struct in_addr {
 	uint32_t	s_addr;
-} in_addr;
+};
+
+typedef struct in_addr in_addr;
+
+typedef uint16_t in_port_t;
+
+struct sockaddr_in {
+	struct in_addr	sin_addr;
+	in_port_t	sin_port;
+};
+
+extern int inet_aton ( const char *cp, struct in_addr *inp );
 
 #endif	/* _IN_H */