Resolve server_abbrev conflict between terminal and FTP servers

These should've been static to begin with, like the other servers. Explains why FTP error message are with "term" as the server.

src/sbbs3/ftpsrvr.c

@@ -49,7 +49,7 @@
 /* Constants */
 
 #define FTP_SERVER				"Synchronet FTP Server"
-const char* server_abbrev = "ftp";
+static const char* server_abbrev = "ftp";
 
 #define ANONYMOUS				"anonymous"
 

src/sbbs3/main.cpp

@@ -41,7 +41,7 @@
 //---------------------------------------------------------------------------
 
 #define TELNET_SERVER "Synchronet Terminal Server"
-const char* server_abbrev = "term";
+static const char* server_abbrev = "term";
 
 #define TIMEOUT_THREAD_WAIT		60			// Seconds (was 15)
 #define IO_THREAD_BUF_SIZE	   	20000		// Bytes