- Add in_init() and move some functions, variables and sysctls into in.c
  where they belong to.  Make some functions and variables static.
- ip_input.c: reduce some #ifdefs, cleanup a little.
- Move some sysctls into ip_flow.c as they belong there.

No functional change.
Move udp6_input(), udp6_sendup(), udp6_realinput() and udp6_input_checksum()
from udp_usrreq.c to udp6_usrreq.c where they belong.  No functional change.
- Make ip_setmoptions(), ip_getmoptions() and ip_pcbopts() static.
- ip_output: eliminate 7th variadic argument; IP_RETURNMTU is flag
  always used to store MTU size into struct inpcb::inp_errormtu.
- Clean up these routines: reduce #ifdefs, variable scopes, etc.
Fix the assert in the previous commit.
PR/48831: Jörg Grundmann: Synaptics Touch pad (ClickPad) and
Klick-by-tap-gestures do not work
Define hacked version of END() in addition to ENTRY().
Put missing END() markers to set ELF symbol size.
Put missing END() markers to set ELF symbol size.
Fix previous.
Put missing END() markers to set ELF symbol size.
No functional change:
- sort in PCI capability ID order.
- add comments.
Make this compile. Hi rmind!