face: add missing out-of-class definition of Transport::MIN_MTU

Also fix a type mismatch in Transport::m_sendQueueCapacity

Change-Id: I5b316917f5088587aefaa1bbb67efe017b77c155
diff --git a/daemon/face/transport.cpp b/daemon/face/transport.cpp
index 457e162..c08990a 100644
--- a/daemon/face/transport.cpp
+++ b/daemon/face/transport.cpp
@@ -31,6 +31,8 @@
 
 NFD_LOG_INIT(Transport);
 
+const ssize_t Transport::MIN_MTU;
+
 std::ostream&
 operator<<(std::ostream& os, TransportState state)
 {