MFC: (1.26) Fix a number of minor bugs in the VLAN code:

• Initialize the "struct sockaddr_dl sdl" correctly in vlan_setmulti().

• The driver used to call malloc(..., M_NOWAIT), but to not check the return value. Change malloc(..., M_NOWAIT) to malloc(..., M_WAITOK) because the corresponding part of code is called from the upper half of the kernel only.

• Make sure a parent interface is up and running before invoking its if_start() routine in order to avoid system panic.

• Do not copy all the flags from a parent mindlessly.

• Do not call if_down() on a parent interface if it's already down. Call if_down() at splimp because if_down() needs that.

Approved by: jkh