Fix a concurrency bug in SPDY settings.

We were making a copy of the streams HashMap so that we could
iterate it safely after releasing our lock. But we weren't
actually using that copy when iterating. Whoops!

Fixes https://github.com/square/okhttp/issues/1119
Merge pull request #1122 from square/jwilson_1103_use_copy

Fix a concurrency bug in SPDY settings.