Suggested diff for src/inject.cc, for type consistency

[schongallam]

Minor issue here, but src/inject.cc will not compile with clang++ due to the following error:

/usr/bin/clang++ -DHAVE_CONFIG_H -I. -I..  -I../lib   -fsanitize=address -fno-omit-frame-pointer -fno-rtti -fno-exceptions -W -Wall -MT inject.o -MD -MP -MF .deps/inject.Tpo -c -o inject.o inject.cc
inject.cc:211:3: error: non-constant-expression cannot be narrowed from type 'size_t' (aka 'unsigned long') to 'unsigned int' in initializer list [-Wc++11-narrowing]
  211 |   X(Sender,            T,F,F,F,F), // 0
      |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Two workarounds are:

1. compile with -Wno-c++11-narrowing
2. compile with -std=c++03

The following diff would avoid these workarounds, and, I propose, would be a preferable general practice for type consistency:

@@ -150,7 +150,7 @@
 {
   // member information
   const char* name;
-  unsigned length;
+  size_t length;
   bool is_address;
   bool is_recipient;
   bool is_sender;