routing: use unique_ptr for signal container

Change-Id: I1912f8630d0e26d8c25c2050208f6b8b0ffd9009
refs: #4268
diff --git a/src/route/name-prefix-table.cpp b/src/route/name-prefix-table.cpp
index bd7269a..4f9d91d 100644
--- a/src/route/name-prefix-table.cpp
+++ b/src/route/name-prefix-table.cpp
@@ -33,7 +33,8 @@
 
 INIT_LOGGER("NamePrefixTable");
 
-NamePrefixTable::NamePrefixTable(Nlsr& nlsr, std::shared_ptr<AfterRoutingChange>& afterRoutingChangeSignal)
+NamePrefixTable::NamePrefixTable(Nlsr& nlsr,
+                                 std::unique_ptr<AfterRoutingChange>& afterRoutingChangeSignal)
   : m_nlsr(nlsr)
 {
   m_afterRoutingChangeConnection = afterRoutingChangeSignal->connect(