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.

rtl837x_common.h

@@ -8,6 +8,7 @@
 #define SYS_TICK_HZ 200
 
 #define CPU_PORT        9
+#define NUL			'\0'
 
 // Define Port-masks for 9-port devices and 6-port devices
 #define PMASK_9		0x1ff
@@ -140,6 +141,7 @@ void itoa(uint8_t v);
 void print_sfr_data(void);
 void print_phy_data(void);
 void print_cmd_prompt(void);
+void print_phys_port(uint8_t port);
 void phy_write_mask(uint16_t phy_mask, uint8_t dev_id, uint16_t reg, uint16_t v);
 void phy_write(uint8_t phy_id, uint8_t dev_id, uint16_t reg, uint16_t v);
 void phy_read(uint8_t phy_id, uint8_t dev_id, uint16_t reg);