Consolidate DHCP v4 and V6 implementation. No functional change intended

The DHCP proxy and VSS information maintained by VPP is the same for v4 and v6, so we can manage this state using the same code.
Packet handling is cleary different, so this is kept separate.

Change-Id: I10f10cc1f7f19debcd4c4b099c6de64e56bb0c69
Signed-off-by: Neale Ranns <nranns@cisco.com>
diff --git a/src/vnet.am b/src/vnet.am
index 70f1e7e..64484e1 100644
--- a/src/vnet.am
+++ b/src/vnet.am
@@ -674,7 +674,7 @@
  vnet/dhcp/dhcp_api.c
 
 nobase_include_HEADERS +=			\
- vnet/dhcp/client.h					\
+ vnet/dhcp/client.h				\
  vnet/dhcp/dhcp.api.h
 
 API_FILES += vnet/dhcp/dhcp.api
@@ -683,13 +683,16 @@
 # DHCP proxy
 ########################################
 libvnet_la_SOURCES +=				\
- vnet/dhcp/proxy_node.c				\
- vnet/dhcp/proxy.h
+ vnet/dhcp/dhcp6_proxy_node.c                   \
+ vnet/dhcp/dhcp4_proxy_node.c			\
+ vnet/dhcp/dhcp_proxy.c
 
 nobase_include_HEADERS +=			\
- vnet/dhcp/packet.h				\
- vnet/dhcp/proxy.h				\
- vnet/dhcp/proxy_error.def
+ vnet/dhcp/dhcp4_packet.h		        \
+ vnet/dhcp/dhcp6_packet.h		        \
+ vnet/dhcp/dhcp_proxy.h				\
+ vnet/dhcp/dhcp6_proxy_error.def                \
+ vnet/dhcp/dhcp4_proxy_error.def
 
 ########################################
 # ipv6 segment routing
@@ -710,17 +713,6 @@
 API_FILES += vnet/sr/sr.api
 
 ########################################
-# DHCPv6 proxy
-########################################
-libvnet_la_SOURCES +=				\
- vnet/dhcpv6/proxy_node.c
-
-nobase_include_HEADERS +=			\
- vnet/dhcpv6/packet.h				\
- vnet/dhcpv6/proxy.h				\
- vnet/dhcpv6/proxy_error.def
-
-########################################
 # IPFIX / netflow v10
 ########################################
 libvnet_la_SOURCES +=				\