openssl: reduce memory consumption

SSL records may be as large as 16K, but are typically < 2K.  In
addition, a historic bug in Windows allowed records to be as large
32K.  OpenSSL statically allocates read and write buffers (34K and
18K respectively) used for processing records.

With this patch, OpenSSL statically allocates 4K + 4K buffers, with
the option of dynamically growing buffers to 34K + 4K, which is a
saving of 44K per connection for the typical case.

This patch is taken from the Android Open Source Project.