tcp: Fix getcred

- Migrate to the target cpu before looking up tcp inpcb.
- Save a copy of the ucred then do SYSCTL_OUT, which could block.
  It is not MPSAFE to do the SYSCTL_OUT even on the target CPU;
  the socket might be ripped when SYSCTL_OUT blocked.
udp: Simplify getcred

- No need to compare cpuid before calling lwkt_migratecpu(), which
  does necessary check itself.
- Streamline the code path a little bit.
Remove csa.4. It is really snd_csa.4 and a csa.4 MLINK will be created.
tools/netrate/netperf: Switch to err(3)
bpf: Use uint32_t for scratch memory.

It is never used as signed array.

Dragonfly-issue: http://bugs.dragonflybsd.org/issues/2722
Submitted-by: guy
localdaemons should care for scripts dependencies in $local_startup too