Fix the return size of aa_getprocattr

aa_getprocattr is returning the size of the buffer not the size of the
data read that it is supposed to return.  Also update the man page to
reflect the return value as documented in the functions, and update
the test cases to check the return value.

Signed-off-by: John Johansen <john.johansen@canonical.com>
Steve Beattie <sbeattie@ubuntu.com>

libraries/libapparmor/src/kernel_interface.c

@@ -280,11 +280,10 @@ int aa_getprocattr(pid_t tid, const char *attr, char **buf, char **mode)
 		free(buffer);
 		*buf = NULL;
 		*mode = NULL;
-		size = -1;
 	} else
 		*buf = buffer;
 
-	return size;
+	return rc;
 }
 
 static int setprocattr(pid_t tid, const char *attr, const char *buf, int len)