Add discrete FTPControl and FTPData protocol types. (#1916)

* Split FTP protocol type into FTPControl and FTPData to differentiate between channels.

* Docs update.

* Lint

* Fixed FTP capitalization.

* Fix FTPData usage.

Author: Dimi1010

Packet++/header/FtpLayer.h

@@ -14,9 +14,9 @@ namespace pcpp
 	{
 	protected:
 		FtpLayer(uint8_t* data, size_t dataLen, Layer* prevLayer, Packet* packet)
-		    : SingleCommandTextProtocol(data, dataLen, prevLayer, packet, FTP) {};
+		    : SingleCommandTextProtocol(data, dataLen, prevLayer, packet, FTPControl) {};
 		FtpLayer(const std::string& command, const std::string& option)
-		    : SingleCommandTextProtocol(command, option, FTP) {};
+		    : SingleCommandTextProtocol(command, option, FTPControl) {};
 
 	public:
 		/// A static method that checks whether the port is considered as FTP control
@@ -447,7 +447,7 @@ namespace pcpp
 		FtpDataLayer(uint8_t* data, size_t dataLen, Layer* prevLayer, Packet* packet)
 		    : PayloadLayer(data, dataLen, prevLayer, packet)
 		{
-			m_Protocol = FTP;
+			m_Protocol = FTPData;
 		};
 
 		/// @return Returns the protocol info as readable string

Packet++/header/ProtocolType.h

@@ -163,8 +163,8 @@ namespace pcpp
 	/// Telnet Protocol
 	const ProtocolType Telnet = 40;
 
-	/// File Transfer (FTP) Protocol
-	const ProtocolType FTP = 41;
+	/// File Transfer (FTP) Protocol - Control channel
+	const ProtocolType FTPControl = 41;
 
 	/// ICMPv6 protocol
 	const ProtocolType ICMPv6 = 42;
@@ -223,6 +223,12 @@ namespace pcpp
 	/// Diagnostic over IP protocol (DOIP)
 	const ProtocolType DOIP = 59;
 
+	/// File Transfer Protocol (FTP) Data channel
+	const ProtocolType FTPData = 60;
+
+	/// FTP protocol family (FTPControl and FtpData protocols)
+	const ProtocolTypeFamily FTP = 0x3c29;
+
 	/// An enum representing OSI model layers
 	enum OsiModelLayer
 	{