sdes: fix SdesNegotiator::negotiate()

SdesNegotiator::negotiate() does an invalid check on given offered crypto-suite.
The current setup is made in a way that this function always returns
the remote crypto suite, supported or not! Dangerous.

This patch fixes that by correctly comparing crypto-suite names.

Change-Id: I0ef022486e00b5fef91d2552b83d57463282a683
Tuleap: #747

src/sip/sdes_negotiator.cpp

@@ -166,7 +166,7 @@ SdesNegotiator::negotiate(const std::vector<std::string>& attributes) const
         auto cryptoAttributeVector(parse(attributes));
         for (const auto& iter_offer : cryptoAttributeVector) {
             for (const auto& iter_local : localCapabilities_) {
-                if (iter_offer.getCryptoSuite().compare(iter_local.name))
+                if (iter_offer.getCryptoSuite() == iter_local.name)
                     return iter_offer;
             }
         }