Improve stop-bits messages in serial setup.

On Windows, due to a copy-paste goof, the message that should have
read "Configuring n stop bits" instead ended with "data bits".

While I'm here, I've arranged that the "1 stop bit" case of that
message is in the singular. And then I've done the same thing again on
Unix, because I noticed that message was unconditionally plural too.

(cherry picked from commit bdb7b47a5e)

unix/uxser.c

@@ -199,8 +199,8 @@ static const char *serial_configure(Serial *serial, Conf *conf)
     } else {
         options.c_cflag &= ~CSTOPB;
     }
-    logeventf(serial->logctx, "Configuring %d stop bits",
-              (options.c_cflag & CSTOPB ? 2 : 1));
+    logeventf(serial->logctx, "Configuring %s",
+              (options.c_cflag & CSTOPB ? "2 stop bits" : "1 stop bit"));
 
     options.c_iflag &= ~(IXON|IXOFF);
 #ifdef CRTSCTS

windows/winser.c

@@ -131,12 +131,12 @@ static const char *serial_configure(Serial *serial, HANDLE serport, Conf *conf)
         logeventf(serial->logctx, "Configuring %u data bits", dcb.ByteSize);
 
         switch (conf_get_int(conf, CONF_serstopbits)) {
-          case 2: dcb.StopBits = ONESTOPBIT; str = "1"; break;
-          case 3: dcb.StopBits = ONE5STOPBITS; str = "1.5"; break;
-          case 4: dcb.StopBits = TWOSTOPBITS; str = "2"; break;
+          case 2: dcb.StopBits = ONESTOPBIT; str = "1 stop bit"; break;
+          case 3: dcb.StopBits = ONE5STOPBITS; str = "1.5 stop bits"; break;
+          case 4: dcb.StopBits = TWOSTOPBITS; str = "2 stop bits"; break;
           default: return "Invalid number of stop bits (need 1, 1.5 or 2)";
         }
-        logeventf(serial->logctx, "Configuring %s data bits", str);
+        logeventf(serial->logctx, "Configuring %s", str);
 
         switch (conf_get_int(conf, CONF_serparity)) {
           case SER_PAR_NONE: dcb.Parity = NOPARITY; str = "no"; break;