QETH debugging tweak to fix potential unexpected exit crash.

When DBGTRC is enabled and an active/running QETH device is rudely detached (either manually or automatically by release_config @ shutdown/exit), DBGTRC can crash due to dev->group->grp_data being NULL.

This tweak fixes that issue as well as provides a new QETH_DUMP_DATA debugging #define to suppress dumping/tracing of i/o buffers. This new #define is only a temporary stopgap measure only until a more proper 'debug' Hercules command can be designed and written to replace it.