ifupdown.c: allow options to udhcpc to be configurable from .config

This allows more control over options that are passed to udhcpc
that are not configurable via /etc/network/interfaces.

Example: rather than quit when an initial lease isn't found,
you could use "--background" so that udhcpc keeps running and
continually attempts to get an ip.  That way, when you plug in
the ethernet after powering on the device, you'll still get an ip.

networking/Config.in

@@ -858,6 +858,15 @@ config FEATURE_TRACEROUTE_USE_ICMP
 
 source networking/udhcp/Config.in
 
+config IFUPDOWN_UDHCPC_CMD_OPTIONS
+	string "ifup udhcpc command line options"
+	default "-R -n"
+	depends on IFUPDOWN && APP_UDHCPC
+	help
+	  Command line options to pass to udhcpc from ifup.
+	  Intended to alter options not available in /etc/network/interfaces.
+	  (IE: --syslog --background etc...)
+
 config VCONFIG
 	bool "vconfig"
 	default n