res_fax: Fix out of bounds error in update_modem_bits().

ASTERISK-24357 #close
Reported by: Jeremy Laine
Patches:
      res_fax_bounds.patch (license #6561) patch uploaded by Jeremy Laine
	  Modified patch to not use magic numbers.


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.8@423979 65c4cc65-6c06-0410-ace0-fbb531ad65f3

res/res_fax.c

@@ -467,7 +467,7 @@ static int update_modem_bits(enum ast_fax_modems *bits, const char *value)
 		m[i] = NULL;
 	} else {
 		tok = strtok(v, ", ");
-		while (tok && (i < 5)) {
+		while (tok && i < ARRAY_LEN(m) - 1) {
 			m[i++] = tok;
 			tok = strtok(NULL, ", ");
 		}