Complete the initialization of tap_softc before if_attach

Basically we should complete the initializaiton of softc before if_attach
because once if_attach is called if_detach can be called for the softc
before returning from if_attach. In case of tap, mutex_destroy can be
called before mutex_init that comes after if_attach.
groff-1.22.3 out.
bpi uses a different mux feature for gmac
- Use __SHIFTIN macro
- fix CM_DISP_GEN_DI1_COUNTER_RELEASE