Convert CONFIG_KEEP_SERVERADDR to Kconfig

This converts the following to Kconfig:
   CONFIG_KEEP_SERVERADDR

Drop the preprocessor usage also.

Signed-off-by: Simon Glass <sjg@chromium.org>

README

@@ -1138,11 +1138,6 @@ The following options need to be configured:
 		server to contact when using the "tftboot" command.
 		(Environment variable "serverip")
 
-		CONFIG_KEEP_SERVERADDR
-
-		Keeps the server's MAC address, in the env 'serveraddr'
-		for passing to bootargs (like Linux's netconsole option)
-
 - Gateway IP address:
 		CONFIG_GATEWAYIP
 

include/configs/sandbox.h

@@ -25,7 +25,6 @@
 #define CONFIG_SYS_BAUDRATE_TABLE	{4800, 9600, 19200, 38400, 57600,\
 					115200}
 
-#define CONFIG_KEEP_SERVERADDR
 #define CONFIG_UDP_CHECKSUM
 #define CONFIG_TIMESTAMP
 #define CONFIG_BOOTP_SERVERIP

net/Kconfig

@@ -99,4 +99,13 @@ config SERVERIP_FROM_PROXYDHCP_DELAY_MS
 		receiving response from main DHCP server. Has no effect if
 		SERVERIP_FROM_PROXYDHCP is false.
 
+config KEEP_SERVERADDR
+	bool "Write the server's MAC address to 'serveraddr'"
+	default y if SANDBOX
+	help
+	  Keeps the server's MAC address, in the env 'serveraddr'
+	  for passing to bootargs (like Linux's netconsole option). If this is
+	  enabled, when an ARP reply is received, the server's IP address is
+	  written there.
+
 endif   # if NET

net/arp.c

@@ -196,13 +196,12 @@ void arp_receive(struct ethernet_hdr *et, struct ip_udp_hdr *ip, int len)
 		if (!arp_is_waiting())
 			break;
 
-#ifdef CONFIG_KEEP_SERVERADDR
-		if (net_server_ip.s_addr == net_arp_wait_packet_ip.s_addr) {
+		if (IS_ENABLED(CONFIG_KEEP_SERVERADDR) &&
+		    net_server_ip.s_addr == net_arp_wait_packet_ip.s_addr) {
 			char buf[20];
 			sprintf(buf, "%pM", &arp->ar_sha);
 			env_set("serveraddr", buf);
 		}
-#endif
 
 		reply_ip_addr = net_read_ip(&arp->ar_spa);