Updates the FB_COMMAND_SIZE from 64 to the linux max value of 4096 and
updates the relevant unit tests.

BUG=182864081

Test: Update the size check to the existing unit tests

Change-Id: I66b08884a5228e164c22c575a6f6c82a236fece2
diff --git a/fastboot/constants.h b/fastboot/constants.h
index b732c76..f6fc74e 100644
--- a/fastboot/constants.h
+++ b/fastboot/constants.h
@@ -42,7 +42,7 @@
 #define RESPONSE_DATA "DATA"
 #define RESPONSE_INFO "INFO"
 
-#define FB_COMMAND_SZ 64
+#define FB_COMMAND_SZ 4096
 #define FB_RESPONSE_SZ 256
 
 #define FB_VAR_VERSION "version"