session/tcp: filtering improvements

- make allow action explicit (-3)
- add session lookup is_filtered return flag that is set if lookup hit a
  deny filter
- change tcp logic to drop filtered packets when punting is enabled

Change-Id: Ic38f294424663a4e108439b7571511f46f8e0be1
Signed-off-by: Florin Coras <fcoras@cisco.com>
diff --git a/src/vnet/session/session_lookup.h b/src/vnet/session/session_lookup.h
index 00ef19f..1bdf6d1 100644
--- a/src/vnet/session/session_lookup.h
+++ b/src/vnet/session/session_lookup.h
@@ -32,7 +32,8 @@
 						       ip4_address_t * rmt,
 						       u16 lcl_port,
 						       u16 rmt_port, u8 proto,
-						       u32 thread_index);
+						       u32 thread_index,
+						       u8 * is_filtered);
 transport_connection_t *session_lookup_connection4 (u32 fib_index,
 						    ip4_address_t * lcl,
 						    ip4_address_t * rmt,
@@ -43,7 +44,8 @@
 						       ip6_address_t * rmt,
 						       u16 lcl_port,
 						       u16 rmt_port, u8 proto,
-						       u32 thread_index);
+						       u32 thread_index,
+						       u8 * is_filtered);
 transport_connection_t *session_lookup_connection6 (u32 fib_index,
 						    ip6_address_t * lcl,
 						    ip6_address_t * rmt,