libs/libc/net: implement etheraton/ether_aton_r

Reference here:
https://www.freebsd.org/cgi/man.cgi?apropos=0&sektion=3&query=ether_aton&manpath=FreeBSD+7.0-current&format=html

Change-Id: I3e70c985836600837dd61810ba290be59b6e8e6f
Signed-off-by: chao.an <anchao@xiaomi.com>

include/netinet/ether.h

@@ -70,6 +70,8 @@ int ether_ntohost(FAR char *hostname, FAR const struct ether_addr *addr);
 int ether_hostton(FAR const char *hostname, FAR struct ether_addr *addr);
 int ether_line(FAR const char *line, FAR struct ether_addr *addr,
                FAR char *hostname);
+FAR struct ether_addr *ether_aton_r(FAR const char *asc,
+                                    FAR struct ether_addr *addr);
 
 #undef EXTERN
 #ifdef __cplusplus