Don't include heavy STL headers like <algorithm> in header files

This provides a considerable compilation time reduction and most
of these were just using std::copy/fill which can be replaced by
memcpy/memset, as all of their uses were applied to POD types

src/dhcp.cpp

@@ -29,6 +29,7 @@
 
 #include <stdexcept>
 #include <cstring>
+#include <algorithm>
 #include "endianness.h"
 #include "dhcp.h"
 #include "ethernetII.h"