Convert CONFIG_ARP_TIMEOUT to Kconfig

This converts the following to Kconfig:
   CONFIG_ARP_TIMEOUT

Cc: Ramon Fried <rfried.dev@gmail.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/net/Kconfig b/net/Kconfig
index 2ae9d6a..683c2ad 100644
--- a/net/Kconfig
+++ b/net/Kconfig
@@ -8,6 +8,10 @@
 
 if NET
 
+config ARP_TIMEOUT
+	int "Milliseconds before trying ARP again"
+	default 5000
+
 config PROT_UDP
 	bool "Enable generic udp framework"
 	help