CampaignManager: avoid parameter-name clash

The -p parameter is already being used by several campaign servers for
the prune method to restrict to (which was broken in commit
6c120004e), hence allow only --port to choose a different server TCP
port at runtime.

Change-Id: Ia30e40d564e85a9702118dc28df4988ec628e491

src/core/cpn/CampaignManager.hpp

@@ -29,8 +29,8 @@ public:
 	CampaignManager() : m_jobserver(0), m_currentCampaign(0)
 	{
 		fail::CommandLine &cmd = fail::CommandLine::Inst();
-		port = cmd.addOption("p", "port", Arg::Required,
-				     "-p,--port \tListening port of server; no "
+		port = cmd.addOption("", "port", Arg::Required,
+				     "--port \tListening port of server; no "
 				     "value chooses port automatically");
 	}
 	~CampaignManager();