Restore (at least temporarily) SHARED=symlinks in the build includes
stage of buildworld.  This was accidentally included in r251140.

Reported by:	jhb
- As a follow-up to r247565, make firmware images that do not require
  patching at runtime actually const.
- Remove pointless softc members by employing the corresponding constants
  directly.
- Remove pointless returns.
- Remove unnecessary inclusion of opt_device_polling.h.
- Replace an outdated and now bogus comment in bce_tick() with the
  appropriate one.

MFC after:	1 week
Update byacc to 20130304