[net] Add KConfig for net.

components/net/KConfig

+menu "Network stack"
+
+menu "light weight TCP/IP stack"
+config RT_USING_LWIP
+	bool "Enable lwIP stack"
+	default n
+
+	if RT_USING_LWIP
+		choice 
+			prompt "lwIP version"
+			default RT_USING_LWIP141
+			help 
+				Select the lwIP version
+
+			config RT_USING_LWIP141
+				bool "lwIP v1.4.1"
+
+			config RT_USING_LWIP200
+				bool "lwIP v2.0.0"
+		endchoice
+
+		config RT_LWIP_IGMP
+			bool "IGMP protocol"
+			default n
+
+		config RT_LWIP_ICMP
+			bool "ICMP protocol"
+			default y
+
+		config RT_LWIP_SNMP
+			bool "SNMP protocol"
+			default n
+
+		config RT_LWIP_DNS
+			bool "Enble DNS for name resolution"
+			select RT_LWIP_UDP
+			default y
+
+		config RT_LWIP_DHCP
+			bool "Enable alloc ip address through DHCP"
+			select RT_LWIP_UDP
+			default y
+
+		config RT_LWIP_UDP
+			bool "UDP protocol"
+			default y
+
+		config RT_LWIP_TCP
+			bool "TCP protocol"
+			default y
+
+		config RT_LWIP_PPP
+			bool "PPP protocol"
+			default n
+
+		config RT_LWIP_PPPOE
+			bool "PPPoE protocol"
+			default n
+
+		config RT_LWIP_PPPOS
+			bool "PPPoS protocol"
+			default n
+
+		config RT_LWIP_RAW_PCB_NUM
+			int "the number of raw connection"
+			default 4
+
+		config RT_LWIP_UDP_PCB_NUM
+			int "the number of UDP socket"
+			default 4
+
+		if RT_LWIP_TCP
+		config RT_LWIP_TCP_PCB_NUM
+			int "the number of TCP socket"
+			default 4
+
+		config RT_LWIP_TCP_SEG_NUM
+			int "the number of TCP segment"
+			default 4
+
+		config RT_LWIP_TCP_SND_BUF
+			int "the size of send buffer"
+			default 8196
+
+		config RT_LWIP_TCP_WND
+			int "the size of TCP send window"
+			default 8196
+		endif
+
+		config RT_LWIP_TCPTHREAD_PRIORITY
+			int "the priority level value of lwIP thread"
+			default 10
+
+		config RT_LWIP_TCPTHREAD_MBOX_SIZE
+			int "the number of mail in the lwIP thread mailbox"
+			default 8
+
+		config RT_LWIP_TCPTHREAD_STACKSIZE
+			int "the stack size of lwIP thread"
+			default 1024
+
+		config RT_LWIP_REASSEMBLY_FRAG
+			bool "Enable IP reassembly and frag"
+			default n
+
+		config SO_REUSE
+			bool "Enable SO_REUSEADDR option"
+			default n
+
+		config LWIP_SO_RCVTIMEO
+			bool "Enable receive timeout for sockets/netconns and SO_RCVTIMEO processing."
+			default n
+
+		config LWIP_SO_SNDTIMEO
+			bool "Enable send timeout for sockets/netconns and SO_SNDTIMEO processing."
+			default n
+
+		config LWIP_SO_RCVBUF
+			bool "Enable SO_RCVBUF processing"
+			default n
+	endif
+
+endmenu
+
+endmenu