port: report link role and negotiated pause per port

Two per-port MAC status registers that nothing in the firmware reads:
0x6408 says which end is master on a BASE-T link, 0x63FC and 0x6400 say
whether pause was negotiated in each direction. port <n> show prints
both at the end.

The read sits in rtl837x_port.c rather than phy_show(), because these
are MAC registers and phy_show() is skipped for SFP ports. Master/slave
keys off machine.is_sfp[] so it stays off the fibre ports, where the
notion does not apply.

Bit N of each register is chip port N, which is not how
RTL837X_REG_LINKS_STS indexes its bytes a few lines above in the same
header.

cmd_parser.c

@@ -893,7 +893,10 @@ void parse_port(void)
 		print_string_x(port_names[phy_settings.port]);
 		if (!machine.is_sfp[phy_settings.port]) {
 			phy_show(phy_settings.port);
+		} else {
+			write_char('\n');
 		}
+		port_media_show(phy_settings.port);
 	} else if (cmd_compare(2, "name")) {
 		uint8_t i = 0;
 		while ( (i < PORT_NAME_SIZE-1) && (cmd_buffer[cmd_words_b[3] + i] != NUL) ) {