external/boringssl: Sync to b2ff2623a88a65fd4db42d3820f3d8c64e8ab180.

This includes the following changes:

https://boringssl.googlesource.com/boringssl/+log/6d50f475e319de153a43e1dba5a1beca95948c63..b2ff2623a88a65fd4db42d3820f3d8c64e8ab180

Change-Id: I649281e093369d99e863b4882a2ff6a5ad8a64d1
Test: ATP's cts/libcore/gce-net (go/gce-net)
diff --git a/sources.bp b/sources.bp
index 31fd493..99720a5 100644
--- a/sources.bp
+++ b/sources.bp
@@ -56,7 +56,6 @@
         "src/crypto/base64/base64.c",
         "src/crypto/bio/bio.c",
         "src/crypto/bio/bio_mem.c",
-        "src/crypto/bio/buffer.c",
         "src/crypto/bio/connect.c",
         "src/crypto/bio/fd.c",
         "src/crypto/bio/file.c",
@@ -398,6 +397,7 @@
 cc_defaults {
     name: "libssl_sources",
     srcs: [
+        "src/ssl/bio_ssl.c",
         "src/ssl/custom_extensions.c",
         "src/ssl/d1_both.c",
         "src/ssl/d1_lib.c",