ssl: Switch to use_certificate_chain for certificate loading

Replace use_certificate with use_certificate_chain to properly handle
both single certificates and certificate chains. This allows loading
and sending the complete certificate chain during TLS handshake,
improving client validation.
Tested with generate_user_auth.py

Change-Id: I8ef1665307ee2e401901a662ac9ee6df7b50937d
Signed-off-by: Ben Peled <bpeled@nvidia.com>
diff --git a/src/ssl_key_handler.cpp b/src/ssl_key_handler.cpp
index b2a78b8..cc11360 100644
--- a/src/ssl_key_handler.cpp
+++ b/src/ssl_key_handler.cpp
@@ -503,7 +503,7 @@
         boost::system::error_code ec;
 
         boost::asio::const_buffer buf(sslPemFile.data(), sslPemFile.size());
-        mSslContext.use_certificate(buf, boost::asio::ssl::context::pem, ec);
+        mSslContext.use_certificate_chain(buf, ec);
         if (ec)
         {
             return false;