move unix_file_* code to vppinfra

This will allow us to use this code in client libraries without vlib.

Change-Id: I8557b752496841ba588aa36b6082cbe2cd1867fe
Signed-off-by: Damjan Marion <damarion@cisco.com>
diff --git a/src/vlib/unix/main.c b/src/vlib/unix/main.c
index 3a92b2e..ed0631e 100644
--- a/src/vlib/unix/main.c
+++ b/src/vlib/unix/main.c
@@ -60,6 +60,7 @@
 char *vlib_default_runtime_dir = "vlib";
 
 unix_main_t unix_main;
+clib_file_main_t file_main;
 
 static clib_error_t *
 unix_main_init (vlib_main_t * vm)