Add input memory stream class and port some PDUs to use it

src/dot1q.cpp

@@ -33,6 +33,9 @@
 #include "dot1q.h"
 #include "internals.h"
 #include "exceptions.h"
+#include "memory_helpers.h"
+
+using Tins::Memory::InputMemoryStream;
 
 namespace Tins {
 
@@ -45,18 +48,15 @@ Dot1Q::Dot1Q(small_uint<12> tag_id, bool append_pad)
 Dot1Q::Dot1Q(const uint8_t *buffer, uint32_t total_sz) 
 : _append_padding()
 {
-    if(total_sz < sizeof(_header))
-        throw malformed_packet();
-    std::memcpy(&_header, buffer, sizeof(_header));
-    buffer += sizeof(_header);
-    total_sz -= sizeof(_header);
+    InputMemoryStream stream(buffer, total_sz);
+    stream.read(_header);
     
-    if(total_sz) {
+    if (stream) {
         inner_pdu(
             Internals::pdu_from_flag(
                 (Constants::Ethernet::e)payload_type(), 
-                buffer, 
-                total_sz
+                stream.pointer(), 
+                stream.size()
             )
         );
     }