We can not do that:
../../common/io/scsi/adapters/iscsi/iscsi_login.c: In function 'iscsi_login_failure_str':
../../common/io/scsi/adapters/iscsi/iscsi_login.c:2066:3: error: label at end of compound statement
   default:
   ^~~~~~~
cc1: all warnings being treated as errors

Anyhow, it does not really change any behavior.

I mean this change:
@@ -2063,9 +2063,8 @@ iscsi_login_failure_str(uchar_t status_class, uchar_t status_detail)
                switch (status_detail) {
                case 0x00:
                        return ("Login is proceeding okay.");
-               default:
-                       break;
                }
+               break;

Yes, but removing default can rise other questions... well, I do know what you mean - in such case the empty default is ugly, this specific switch would be much better to be replaced by if statement. But then again, I am not too keen about such replacement because then I should dig into iscsi specs to see if there are some responses missed or not, and I do not have time for this:D Which is why I would just let the compiler do its job optimize the proper asm:)

then I should dig into iscsi specs to see if there are some responses missed

I expect that you shouldn't dig, due to removing "default: break" doesn't change behaviour.
Having "default: break;" has the same behaviour as without one and introduces difficulties. Anyway, I mark this a Approved :)