DHCP request fix for Windows Server 2003

Added option CONFIG_BOOTP_DHCP_REQUEST_DELAY. This provides an optional
delay before sending "DHCP Request" in net/bootp.c. Required to overcome
interoperability problems with Windows Server 200x DHCP server when U-Boot
client responds too fast for server to handle.

Signed-off-by: Aras Vaichas <arasv@magtech.com.au>
Signed-off-by: Ben Warren <biggerbadderben@gmail.com>
diff --git a/README b/README
index 5cbe7c1..592d1d8 100644
--- a/README
+++ b/README
@@ -1151,6 +1151,20 @@
 		of the "hostname" environment variable is passed as
 		option 12 to the DHCP server.
 
+		CONFIG_BOOTP_DHCP_REQUEST_DELAY
+
+		A 32bit value in microseconds for a delay between
+		receiving a "DHCP Offer" and sending the "DHCP Request".
+		This fixes a problem with certain DHCP servers that don't
+		respond 100% of the time to a "DHCP request". E.g. On an
+		AT91RM9200 processor running at 180MHz, this delay needed
+		to be *at least* 15,000 usec before a Windows Server 2003
+		DHCP server would reply 100% of the time. I recommend at
+		least 50,000 usec to be safe. The alternative is to hope
+		that one of the retries will be successful but note that
+		the DHCP timeout and retry process takes a longer than
+		this delay.
+
  - CDP Options:
 		CONFIG_CDP_DEVICE_ID