nvmf_tcp: Update R2T accounting stats when aborting command buffers

If a queue pair is destroyed (e.g. due to the TCP connection dropping)
while a host to controller data transfer is in progress, the
pending_r2ts counter can be non-zero. This can later trigger an
assertion failure when the capsule is freed. To fix, update the
relevant R2T accounting stats when aborting active command buffers
during queue pair destruction.

Sponsored by: Chelsio Communications