MINOR: ssl: add defines LISTEN_DEFAULT_CIPHERS and CONNECT_DEFAULT_CIPHERS.

These ones are used to set the default ciphers suite on "bind" lines and
"server" lines respectively, instead of using OpenSSL's defaults. These
are probably mainly useful for distro packagers.
diff --git a/Makefile b/Makefile
index f0533a7..653c083 100644
--- a/Makefile
+++ b/Makefile
@@ -139,6 +139,11 @@
 # Use DEFINE=-Dxxx to set any tunable macro. Anything declared here will appear
 # in the build options reported by "haproxy -vv". Use SILENT_DEFINE if you do
 # not want to pollute the report with complex defines.
+# The following settings might be of interest when SSL is enabled :
+#   LISTEN_DEFAULT_CIPHERS is a cipher suite string used to set the default SSL
+#           ciphers on "bind" lines instead of using OpenSSL's defaults.
+#   CONNECT_DEFAULT_CIPHERS is a cipher suite string used to set the default
+#           SSL ciphers on "server" lines instead of using OpenSSL's defaults.
 DEFINE =
 SILENT_DEFINE =