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
1 file changed