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/udp-channel.cpp b/daemon/face/udp-channel.cpp
index 8804f06..4e91045 100644
--- a/daemon/face/udp-channel.cpp
+++ b/daemon/face/udp-channel.cpp
@@ -29,8 +29,7 @@
 #include "unicast-udp-transport.hpp"
 #include "common/global.hpp"
 
-namespace nfd {
-namespace face {
+namespace nfd::face {
 
 NFD_LOG_INIT(UdpChannel);
 
@@ -197,5 +196,4 @@
   return {true, face};
 }
 
-} // namespace face
-} // namespace nfd
+} // namespace nfd::face