Fix abd_enter/exit_critical wrappers

Commit fc551d7 introduced the wrappers abd_enter_critical() and
abd_exit_critical() to mark critical sections.  On Linux these are
implemented with the local_irq_save() and local_irq_restore() macros
which set the 'flags' argument when saving.  By wrapping them with
a function the local variable is no longer set by the macro and is
no longer properly restored.

Convert abd_enter_critical() and abd_exit_critical() to macros to
resolve this issue and ensure the flags are properly restored.

Reviewed-by: Matthew Ahrens <mahrens@delphix.com>
Reviewed-by: Brian Atkinson <batkinson@lanl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #10332

module/os/freebsd/zfs/abd_os.c

@@ -419,15 +419,3 @@ abd_iter_unmap(struct abd_iter *aiter)
 	aiter->iter_mapaddr = NULL;
 	aiter->iter_mapsize = 0;
 }
-
-void
-abd_enter_critical(unsigned long flags)
-{
-	critical_enter();
-}
-
-void
-abd_exit_critical(unsigned long flags)
-{
-	critical_exit();
-}

module/os/linux/zfs/abd_os.c

@@ -803,18 +803,6 @@ abd_iter_unmap(struct abd_iter *aiter)
 	aiter->iter_mapsize = 0;
 }
 
-void
-abd_enter_critical(unsigned long flags)
-{
-	local_irq_save(flags);
-}
-
-void
-abd_exit_critical(unsigned long flags)
-{
-	local_irq_restore(flags);
-}
-
 #if defined(_KERNEL)
 /*
  * bio_nr_pages for ABD.