Allow @ in T_LABEL_OID

From the bug report:
  Per PacketCable 1.5 spec, if BASIC or HYBRID mode are used. There are
  a default snmpcommunityname call "@mtaprov" enable.

  However, docsis compiler failed to compile the MTA config with "@"
  symbol in.

  It can decode the file while it fails to encode.

  Here's the samples:
  ***********************************************
  SnmpMibObject snmpCommunityName.'@mtaprov' String "mtaprovrw" ;
  SnmpMibObject snmpTargetAddrTMask.'@mtaprov' HexString 0xffffffff0000 ;
  ***********************************************

http://sf.net/tracker/?func=detail&aid=2127613&group_id=22615&atid=375629

src/docsis_lex.l

@@ -45,7 +45,7 @@ char *tsave;
 ([0-9A-Fa-f][0-9A-Fa-f]:){5}[0-9A-Fa-f][0-9A-Fa-f]  { TSAVE(yytext);yylval.strval=tsave; return T_MAC; 			       }
 
 (\.{1})*([A-Za-z0-9_-]+\.)+[A-Za-z0-9]+	{ TSAVE(yytext);yylval.strval=tsave; return T_LABEL_OID; }
-(\.{1})*([A-Za-z0-9_-]+\.)+'[\[A-Za-z0-9,:_\-\.\]]+'	{ TSAVE(yytext);yylval.strval=tsave; return T_LABEL_OID; }
+(\.{1})*([A-Za-z0-9_-]+\.)+'[\[A-Za-z0-9@,:_\-\.\]]+'	{ TSAVE(yytext);yylval.strval=tsave; return T_LABEL_OID; }
 (\.{1})*([A-Za-z0-9_-]+\.)+((\"{1})*[A-Za-z0-9,:_\-\.]+(\"{1})*)+	{ TSAVE(yytext);yylval.strval=tsave; return T_LABEL_OID; }
 ([0-9]+:){3}[0-9]+\.[0-9]+	{ TSAVE(yytext);yylval.strval=tsave; return T_TIMETICKS; }
 [Mm][Aa][Ii][Nn]        { yylval.strval=yytext;return T_MAIN; }