Summary

show interfaces wwan <name> calls the op-mode backend with
--intf-type=wirelessmodem. That is the legacy interface type from before
T3620. The interface section of WWANIf is wwan, and
Section._intf_under_section() drops every interface whose section does
not match the requested type. So the per-interface command returns no
interface at all.

T5196 already replaced wirelessmodem with wwan for
show interfaces wwan and show interfaces wwan detail, but missed the
per-interface virtualTagNode:

interfaces.py show --intf-name="$4" --intf-type=wirelessmodem

Steps to reproduce

1. Configure a WWAN interface, e.g. set interfaces wwan wwan0 apn internet
2. Run show interfaces wwan wwan0

Expected behavior

Details of wwan0 are displayed, the same as show interfaces wwan detail
shows for it.

Actual behavior

No interface data is shown, because the type filter does not match.

Notes

• Found by code review, not reproduced on hardware.
• Fix: use --intf-type=wwan, consistent with the other two commands in the same file.