Merge upstream/main into the Spanning Tree branch

cmd_parser.c conflicted twice: main rewrote the pvid command around the
new port-separator and atoi helpers, next to the line where this branch
delegates "stp" to stp_parse(). Both belong, so the STP delegation keeps
main's pvid body.

The linker caught what the merge could not see: main changed atoi_byte()
to return the digit count and leave the value in atoi_results_u8, where
it used to return non-zero on failure and write through a pointer. Note
the sense is inverted, so the three calls in rtl837x_stp.c are adjusted
rather than just re-arranged.

rtlplayground.c

@@ -838,6 +838,19 @@ void print_reg(uint16_t reg)
 	print_sfr_data();
 }
 
+// Print the physical port of a logical port number.
+void print_phys_port(uint8_t port)
+{
+	if (port < CPU_PORT)
+		write_char(machine.log_to_phys_port[port] + '0');
+	else if (port == CPU_PORT)
+		print_string("CPU");
+	else {
+		print_string("UNKNOWN ");
+		write_char(port + '0');
+	}
+}
+
 
 /*
 // TODO: This uses 2 DSEG bytes and is not used!
@@ -1276,11 +1289,11 @@ bool sfp_read_field(__xdata char *dst, uint8_t sfp, uint8_t start, uint8_t lengt
 	if (!sfp_read_block(sfp, start, length))
 		return false;
 
-	dst[length] = '\0';
+	dst[length] = NUL;
 	memcpy(dst, sfp_buf, length);
 
 	while (length > 0 && dst[--length] == ' ')
-		dst[length] = '\0';
+		dst[length] = NUL;
 
 	return true;
 }
@@ -2088,7 +2101,7 @@ void check_and_flash_update_image(void)
  * because itohex() is inline and brings its own frame. */
 void set_hostname_default(void)
 {
-	if (hostname[0] != '\0')
+	if (hostname[0] != NUL)
 		return;
 
 	strcpy((__xdata uint8_t *)hostname, "RTLPlayground-");
@@ -2098,7 +2111,7 @@ void set_hostname_default(void)
 	hostname[17] = hex[uip_ethaddr.addr[4] & 0xf];
 	hostname[18] = hex[uip_ethaddr.addr[5] >> 4];
 	hostname[19] = hex[uip_ethaddr.addr[5] & 0xf];
-	hostname[20] = '\0';
+	hostname[20] = NUL;
 }