[CX] Incorrect value for incoming records count metric (in test environment)

This has been observed when running the tests.

Steps to reproduce (occurs in test environment):

• Run a cluster with a single node.
• Load travel-sample bucket
• Create dataset travels1 on travel-sample
• Read the incoming_records_count stats to confirm that 31591 records are loaded
• Rebalance and add another node (links are disconnected, stats are reset to 0)
• Create dataset travels2 on travel-sample
• Read the incoming_records_count stats to confirm that 31591 records are loaded
• Add 2 non-JSON records to travel-sample bucket:
  • upsert travel-sample 1 Not A JSON (cbas command to add records in test framework)
  • upsert travel-sample 2 Not A JSON (cbas command to add records in test framework)
• Read the stats for failed_to_parse_records_count to ensure 2 records failed to be parsed
• Read the stats for incoming_records_count, should report 31593 (31591 + 2 incoming non-JSON), but reported value is 31594 or 31595.

Observations:

• The logs show the 2 non-JSON records sending 4 mutations instead of 2 (2 for each record), which increased the incoming records count to an incorrect value.
• The issue didn't happen on a single node.
• The issue didn't happen on beer-sample bucket for 1024 vbuckets and 64 vbuckets (cbas test config).
• The issue happens on travel-sample bucket for 1024 vbuckets and 64 vbuckets (cbas test config).

Attached logs for both nodes.