Merge bitcoin#18931: net: use CMessageHeader::HEADER_SIZE, add missing include

83da576 net: use CMessageHeader::HEADER_SIZE, add missing include (Jon Atack)

Pull request description:

  as suggested 16 months ago by Gleb Naumenko in bitcoin#15197 (comment).

  `static constexpr CMessageHeader::HEADER_SIZE` is already used in this file, `src/net.cpp`, in 2 instances. This commit replaces the remaining 2 integer values in the file with it and adds the explicit include header.

  Co-authored by: Gleb Naumenko <[email protected]>

ACKs for top commit:
  naumenkogs:
    utACK 83da576
  practicalswift:
    ACK 83da576 -- patch looks correct
  theStack:
    ACK 83da576 -- verified that its just magic number elimination refactoring and additionally checked that all tests pass 👍

Tree-SHA512: 5b915483bca4ea162c259865a1b615d73b88a1b1db3f82db05f770d10b8a42494d948f5b21badbcce2d9efa5915b8cbb6af83073867c23d2f152c0d35ac37b96

Author: fanquake

src/net.cpp

@@ -20,6 +20,7 @@
 #include <net_permissions.h>
 #include <netaddress.h>
 #include <netbase.h>
+#include <protocol.h>
 #include <random.h>
 #include <scheduler.h>
 #include <ui_interface.h>
@@ -757,14 +758,14 @@ int CNode::GetSendVersion() const
 int V1TransportDeserializer::readHeader(Span<const uint8_t> msg_bytes)
 {
     // copy data to temporary parsing buffer
-    unsigned int nRemaining = 24 - nHdrPos;
+    unsigned int nRemaining = CMessageHeader::HEADER_SIZE - nHdrPos;
     unsigned int nCopy = std::min<unsigned int>(nRemaining, msg_bytes.size());
 
     memcpy(&hdrbuf[nHdrPos], msg_bytes.data(), nCopy);
     nHdrPos += nCopy;
 
     // if header incomplete, exit
-    if (nHdrPos < 24)
+    if (nHdrPos < CMessageHeader::HEADER_SIZE)
         return nCopy;
 
     // deserialize to CMessageHeader