Refactor and modernize namespace declarations

Move all unit tests to namespace nfd::tests

Delete unused header core/algorithm.hpp

Change-Id: I5591f0c5f3bb5db67f8b45fae95471f8a555ca68
diff --git a/daemon/face/generic-link-service.hpp b/daemon/face/generic-link-service.hpp
index 0f589a3..be216a7 100644
--- a/daemon/face/generic-link-service.hpp
+++ b/daemon/face/generic-link-service.hpp
@@ -31,8 +31,7 @@
 #include "lp-reassembler.hpp"
 #include "lp-reliability.hpp"
 
-namespace nfd {
-namespace face {
+namespace nfd::face {
 
 /** \brief counters provided by GenericLinkService
  *  \note The type name 'GenericLinkServiceCounters' is implementation detail.
@@ -325,7 +324,6 @@
   return *this;
 }
 
-} // namespace face
-} // namespace nfd
+} // namespace nfd::face
 
 #endif // NFD_DAEMON_FACE_GENERIC_LINK_SERVICE_HPP