Specifically, ccr(4) devices are also children of cxgbe nexus devices.
Rather than making assumptions about the child device's softc, walk
the list of ports from the nexus' softc to determine if a child is a
port in t4_child_location_str(). This fixes a panic when detaching a
ccr device.
Reviewed by: np
MFC after: 1 week
Sponsored by: Chelsio Communications
Differential Revision: https://reviews.freebsd.org/D19399