ifconfig: 802.11: decode more information elements (IEs)

Start dealing with Element ID Extension present (IE T=255) and start
parsing elemants from the Element ID Extension set.

Namely (partially) decode HE_CAPA, HE_OPER, MU_EDCA_PARAM_SET,
and as well as SUP_OP_CLASS.

For length reasons also rename UNKNOWN_ELEMID_%d to ELEMID_%d.

Sponsored by: The FreeBSD Foundation
MFC after: 3 days
Reviewed by: adrian
Differential Revision: https://reviews.freebsd.org/D50678