Activate filesystem features only in syncing context

When activating filesystem features after receiving a snapshot, do
so only in syncing context.

Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Reviewed-by: Richard Yao <richard.yao@alumni.stonybrook.edu>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: George Amanakis <gamanakis@gmail.com>
Closes openzfs#14304
Closes openzfs#14252
(cherry picked from commit eee9362)

tests/runfiles/common.run

@@ -822,8 +822,8 @@ tests = ['recv_dedup', 'recv_dedup_encrypted_zvol', 'rsend_001_pos',
     'send-c_lz4_disabled', 'send-c_recv_lz4_disabled',
     'send-c_mixed_compression', 'send-c_stream_size_estimate',
     'send-c_embedded_blocks', 'send-c_resume', 'send-cpL_varied_recsize',
-    'send-c_recv_dedup', 'send-L_toggle',
-    'send_encrypted_incremental.ksh', 'send_encrypted_hierarchy',
+    'send-c_recv_dedup', 'send-L_toggle', 'send_encrypted_hierarchy',
+    'send_encrypted_incremental.ksh',
     'send_encrypted_props', 'send_encrypted_truncated_files',
     'send_freeobjects', 'send_realloc_files',
     'send_realloc_encrypted_files', 'send_spill_block', 'send_holds',