scsi: target: iscsi: Avoid in_interrupt() usage in iscsit_close_session()

iscsit_close_session() uses in_interrupt() to decide if it needs to check
the return value of iscsit_check_session_usage_count() if it was not able
to sleep.

The usage of in_interrupt() in drivers is phased out and Linus clearly
requested that code which changes behaviour depending on context should
either be separated or the context be conveyed in an argument passed by the
caller, which usually knows the context.

iscsit_close_session() has two callers:

 - iscsit_handle_time2retain_timeout()
   A timer_list callback.

 - iscsit_close_connection()
   Runs in preemptible context, acquires a mutex.

Add an argument to iscsit_close_session() indicating if sleeping is
possible.

Link: https://lore.kernel.org/r/20201220203638.43615-2-bigeasy@linutronix.de


Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>