external/boringssl: add P-521 back into the ClientHello.

This change does strange things to servers which take it as clue that
nothing to do with P-521 is acceptable just because it's missing from
the ClientHello.

Hopefully for the next Android release we can remove this and replace it
with the support for the CFRG curves.

Bug: 20634927
Change-Id: I1d1a65cd82f68ac6d8da5560075cbacaebf539e1
diff --git a/src/ssl/t1_lib.c b/src/ssl/t1_lib.c
index 433a647..58b7f04 100644
--- a/src/ssl/t1_lib.c
+++ b/src/ssl/t1_lib.c
@@ -358,6 +358,9 @@
 static const uint16_t eccurves_default[] = {
     23, /* X9_62_prime256v1 */
     24, /* secp384r1 */
+#if defined(ANDROID)
+    25, /* secp521r1 */
+#endif
 };
 
 int tls1_ec_curve_id2nid(uint16_t curve_id) {