Replace a use of index with strchr.

Change-Id: I2c1238bc1bd0945533712d0d74a761721b8408a3
diff --git a/libcore/luni/src/main/native/org_apache_harmony_luni_platform_OSNetworkSystem.cpp b/libcore/luni/src/main/native/org_apache_harmony_luni_platform_OSNetworkSystem.cpp
index 12c3dd9..4680ca6 100644
--- a/libcore/luni/src/main/native/org_apache_harmony_luni_platform_OSNetworkSystem.cpp
+++ b/libcore/luni/src/main/native/org_apache_harmony_luni_platform_OSNetworkSystem.cpp
@@ -493,7 +493,7 @@
 
     // Accept IPv6 addresses (only) in square brackets for compatibility.
     if (ipString[0] == '[' && ipString[byteCount - 1] == ']' &&
-            index(ipString, ':') != NULL) {
+            strchr(ipString, ':') != NULL) {
         memmove(ipString, ipString + 1, byteCount - 2);
         ipString[byteCount - 2] = '\0';
     }