Fix errata #4 handling for resuming streams

Currently, the handling for errata #4 has two issues which allow
the checks for this issue to be bypassed using resumable sends.
The first issue is that drc->drc_fromsnapobj is not set in the
resuming code as it is in the non-resuming code. This causes
dsl_crypto_recv_key_check() to skip its checks for the
from_ivset_guid. The second issue is that resumable sends do not
clean up their on-disk state if they fail the checks in
dmu_recv_stream() that happen before any data is received.

As a result of these two bugs, a user can attempt a resumable send
of a dataset without a from_ivset_guid. This will fail the initial
dmu_recv_stream() checks, leaving a valid resume state. The send
can then be resumed, which skips those checks, allowing the receive
to be completed.

This commit fixes these issues by setting drc->drc_fromsnapobj in
the resuming receive path and by ensuring that resumablereceives
are properly cleaned up if they fail the initial dmu_recv_stream()
checks.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tom Caputi <tcaputi@datto.com>
Closes #9818 
Closes #9829

include/sys/dmu_recv.h

@@ -49,6 +49,7 @@ typedef struct dmu_recv_cookie {
 	uint64_t drc_featureflags;
 	boolean_t drc_force;
 	boolean_t drc_resumable;
+	boolean_t drc_should_save;
 	boolean_t drc_raw;
 	boolean_t drc_clone;
 	boolean_t drc_spill;