interest+data: add setSignatureValue() overload that takes a span

Change-Id: Ic6a55bf91e0d62760fb75a643cd7dbc1e92c31f2
diff --git a/tests/unit/security/certificate.t.cpp b/tests/unit/security/certificate.t.cpp
index d0633f0..a9df438 100644
--- a/tests/unit/security/certificate.t.cpp
+++ b/tests/unit/security/certificate.t.cpp
@@ -129,12 +129,12 @@
 generateFakeSignature(Data& data)
 {
   SignatureInfo signatureInfo(Block{SIG_INFO});
-  signatureInfo.setKeyLocator(KeyLocator(Name("/ndn/site1/KEY/ksk-2516425377094")));
+  signatureInfo.setKeyLocator(Name("/ndn/site1/KEY/ksk-2516425377094"));
   signatureInfo.setValidityPeriod(ValidityPeriod(time::fromIsoString("20141111T050000"),
                                                  time::fromIsoString("20141111T060000")));
 
   data.setSignatureInfo(signatureInfo);
-  data.setSignatureValue(make_shared<Buffer>(SIG_VALUE, sizeof(SIG_VALUE)));
+  data.setSignatureValue(SIG_VALUE);
 }
 
 BOOST_AUTO_TEST_CASE(Construction)