- Switch the "net.inet.tcp.reass.cursegments" and

- Switch the "net.inet.tcp.reass.cursegments" and
  "net.inet.tcp.reass.maxsegments" sysctl variables to be based on UMA zone
  stats. The value returned by the cursegments sysctl is approximate owing to
  the way in which uma_zone_get_cur is implemented.

- Discontinue use of V_tcp_reass_qsize as a global reassembly segment count
  variable in the reassembly implementation. The variable was used without
  proper synchronisation and was duplicating accounting done by UMA already. The
  lack of synchronisation was particularly problematic on SMP systems
  terminating many TCP sessions, resulting in poor TCP performance for
  connections with non-zero packet loss.

Sponsored by:	FreeBSD Foundation
Reviewed by:	andre, gnn, rpaulo (as part of a larger patch)
MFC after:	2 weeks