res_fax: check_modem_rate() returned incorrect rate for V.27

According to the new standard for V.27 and V.32 they are able to transmit
at a bit rate of 4,800 or 9,600.  The check_mode_rate function needed to be
updated to reflect this.  Also, because of this change the default 'minrate'
value was updated to be 4800.

(closes issue ASTERISK-22790)
Reported by: Paolo Compagnini
Patches:
     res_fax.txt uploaded by looserouting (license 6548)
........

Merged revisions 405656 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 405693 from http://svn.asterisk.org/svn/asterisk/branches/11
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Merged revisions 405694 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@405695 65c4cc65-6c06-0410-ace0-fbb531ad65f3

configs/res_fax.conf.sample

@@ -8,8 +8,8 @@ maxrate=14400
 
 ; Minimum Transmission Rate
 ; Possible values are { 2400 | 4800 | 7200 | 9600 | 12000 | 14400 }
-; Set this value to the minimum desired transfer rate.  Default: 2400
-minrate=2400
+; Set this value to the minimum desired transfer rate.  Default: 4800
+minrate=4800
 
 ; Send Progress/Status events to manager session
 ; Manager events with 'call' class permissions will receive events indicating the

res/res_fax.c

@@ -333,7 +333,7 @@ struct fax_module {
 };
 static AST_RWLIST_HEAD_STATIC(faxmodules, fax_module);
 
-#define RES_FAX_MINRATE 2400
+#define RES_FAX_MINRATE 4800
 #define RES_FAX_MAXRATE 14400
 #define RES_FAX_STATUSEVENTS 0
 #define RES_FAX_MODEM (AST_FAX_MODEM_V17 | AST_FAX_MODEM_V27 | AST_FAX_MODEM_V29)
@@ -708,7 +708,7 @@ static int check_modem_rate(enum ast_fax_modems modems, unsigned int rate)
 {
 	switch (rate) {
 	case 2400:
-		if (!(modems & (AST_FAX_MODEM_V27 | AST_FAX_MODEM_V34))) {
+		if (!(modems & (AST_FAX_MODEM_V34))) {
 			return 1;
 		}
 		break;
@@ -718,11 +718,15 @@ static int check_modem_rate(enum ast_fax_modems modems, unsigned int rate)
 		}
 		break;
 	case 7200:
-	case 9600:
 		if (!(modems & (AST_FAX_MODEM_V17 | AST_FAX_MODEM_V29 | AST_FAX_MODEM_V34))) {
 			return 1;
 		}
 		break;
+	case 9600:
+		if (!(modems & (AST_FAX_MODEM_V17 | AST_FAX_MODEM_V27 | AST_FAX_MODEM_V29 | AST_FAX_MODEM_V34))) {
+			return 1;
+		}
+		break;
 	case 12000:
 	case 14400:
 		if (!(modems & (AST_FAX_MODEM_V17 | AST_FAX_MODEM_V34))) {