tcp: build image with TCP_DEBUG_ALWAYS via make

Add cmake option to enable TCP_DEBUG_ALWAYS.
make rebuild VPP_EXTRA_CMAKE_ARGS=-DVPP_TCP_DEBUG_ALWAYS=ON
make rebuild VPP_EXTRA_CMAKE_ARGS=-DVPP_TCP_DEBUG_ALWAYS=OFF

Type: improvement

Signed-off-by: Steven Luong <sluong@cisco.com>
Change-Id: I911a8d615f76516ae0a988bc6135c3b0d8fcb3df
diff --git a/src/vnet/tcp/tcp_debug.h b/src/vnet/tcp/tcp_debug.h
index 03240c6..a0bdaa3 100644
--- a/src/vnet/tcp/tcp_debug.h
+++ b/src/vnet/tcp/tcp_debug.h
@@ -23,7 +23,11 @@
  * debug configuration. Comes with some overhead so it's not recommended for
  * production/performance scenarios. Takes priority over TCP_DEBUG_ENABLE.
  */
+#ifdef VPP_TCP_DEBUG_ALWAYS
+#define TCP_DEBUG_ALWAYS (1)
+#else
 #define TCP_DEBUG_ALWAYS (0)
+#endif
 /**
  * Build debugging infra only if enabled. Debug components controlled via
  * macros that follow.