Fix Android keystore support for older keystore_get.h

Fix Android keystore support for older keystore_get.h

This is an "inline" function, in the header file. So it's about the build
environment you use for building openconnect, not the runtime environment.

It was fixed by the following commit in android/frameworks/base:

commit c741a2fe41ea33fc386a4d5b932cc081aa92a18c
Author: Chia-chi Yeh <chiachi@android.com>
Date:   Thu Sep 30 15:17:58 2010 +0800

    KeyStore: Fix the return value when send() or recv() has an error.

    Change-Id: I20a63c76bd29b1a9f8959a6c4fe5a5b8a9a971b4

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>