Wrong byte counter after BPF truncation: totlen -= len should be totlen = len

Summary

ng_bpf_rcvdata (:414-418): if(len<totlen){m_adj(m,-(totlen-len));totlen-=len;} m_adj trims (totlen-len) bytes so pkthdr.len==len correct. But totlen-=len makes totlen=(orig-len) = bytes stripped not new length. Corrupted totlen consumed as xmitOctets delta :429 dhip->stats.xmitOctets+=totlen. 1500B packet filter returns 30 -> xmitOctets+=1470 instead of 30. Forwarded packet correct only accounting wrong. netgraph7 fixed :486 (totlen=len) legacy never updated. No security impact totlen consumed only as u_int added to u_int64_t stat no length-driven copy. Fix: totlen=len.