Add ability to set link state with ip

Exposes existing netlink operations to modify link state of devices.
diff --git a/ip/ipaddress.c b/ip/ipaddress.c
index aea1a81..9306a37 100644
--- a/ip/ipaddress.c
+++ b/ip/ipaddress.c
@@ -131,6 +131,16 @@
 		fprintf(f, "state %s ", oper_states[state]);
 }
 
+int get_operstate(const char *name)
+{
+	int i;
+
+	for (i = 0; i < sizeof(oper_states)/sizeof(oper_states[0]); i++)
+		if (strcasecmp(name, oper_states[i]) == 0)
+			return i;
+	return -1;
+}
+
 static void print_queuelen(FILE *f, struct rtattr *tb[IFLA_MAX + 1])
 {
 	int qlen;