Add an option to allow unknown ALPN protocols.

We received an external request to add an option to undo the check added
in 3e51757de2bf9beef7d249f22d255e4dd9ddb012.

Change-Id: Ifdd4b07705f2fa3d781d775d5cd139ea72d36734
Reviewed-on: https://boringssl-review.googlesource.com/14644
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
diff --git a/ssl/ssl_lib.c b/ssl/ssl_lib.c
index 17e6521..7adf103 100644
--- a/ssl/ssl_lib.c
+++ b/ssl/ssl_lib.c
@@ -1753,6 +1753,9 @@
   }
 }
 
+void SSL_CTX_set_allow_unknown_alpn_protos(SSL_CTX *ctx, int enabled) {
+  ctx->allow_unknown_alpn_protos = !!enabled;
+}
 
 void SSL_CTX_set_tls_channel_id_enabled(SSL_CTX *ctx, int enabled) {
   ctx->tlsext_channel_id_enabled = !!enabled;