bcachefs: print op->nonce on data update inconsistency

"nonce inconstancy" is popping up again, causing us to go emergency
read-only.

This one looks less serious, i.e. specific to the encryption path and
not indicative of a data corruption bug. But we'll need more info to
track it down.

Signed-off-by: Kent Overstreet <[email protected]>

Author: Kent Overstreet

fs/bcachefs/data_update.c

@@ -340,6 +340,7 @@ static int __bch2_data_update_index_update(struct btree_trans *trans,
 			struct printbuf buf = PRINTBUF;
 
 			prt_str(&buf, "about to insert invalid key in data update path");
+			prt_printf(&buf, "\nop.nonce: %u", m->op.nonce);
 			prt_str(&buf, "\nold: ");
 			bch2_bkey_val_to_text(&buf, c, old);
 			prt_str(&buf, "\nk:   ");