vnet: Disable tuntap build on not Linux

tuntap requires porting on FreeBSD, only build on Linux for now.

Type: improvement
Change-Id: I448c462b31f3bc06f291a95d0ff5df9d6f8f24b8
Signed-off-by: Tom Jones <thj@freebsd.org>
diff --git a/src/vnet/CMakeLists.txt b/src/vnet/CMakeLists.txt
index 516a5fa..973a6c9 100644
--- a/src/vnet/CMakeLists.txt
+++ b/src/vnet/CMakeLists.txt
@@ -1107,6 +1107,7 @@
 
 # FIXME: unix/hgshm.c
 
+if("${CMAKE_SYSTEM_NAME}" STREQUAL "Linux")
 list(APPEND VNET_SOURCES
   unix/gdb_funcs.c
   unix/tuntap.c
@@ -1115,6 +1116,7 @@
 list(APPEND VNET_HEADERS
   unix/tuntap.h
 )
+endif()
 
 ##############################################################################
 # FIB