scoutfs: add net header printk args

We have macros for creating and printing trace arguments for our network
header struct.  Add a macro for making simple printk call args for
normal formatted output callers.

Signed-off-by: Zach Brown <zab@versity.com>

kmod/src/server.h

@@ -23,6 +23,8 @@ do {									\
 	__entry->name##_port
 
 #define SNH_FMT	"id %llu data_len %u msg %u cmd %u error %u"
+#define SNH_ARG(nh) le64_to_cpu((nh)->id), le16_to_cpu((nh)->data_len), \
+		    (nh)->msg, (nh)->cmd, (nh)->error
 
 #define snh_trace_define(name)		\
 	__field(__u64, name##_id)	\