MFC: if_re.c 1.77, 1.86, 1.94
MFC: if_re.c 1.77, 1.86, 1.94

- Correctly set IFCAP_VLAN_HWCSUM as re(4) can do VLAN tagging/checksum
  offloading in hardware.
- Correctly set media header length for VLAN.
- Use taskqueue_drain() to wait for any pending tasks to complete rather
  than just pausing for a second.
- Initialize the rl_vlanctl field of the descriptors to zero (in order
  to clear RL_TDESC_VLANCTL_TAG).

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