Fix ISP_FC_LIP and ISP_RESCAN on big-endian 64-bit systems.

For _IO() ioctls, addr is a pointer to uap->data which is a caddr_t.
When the caddr_t stores an int, dereferencing addr as an (int *) results
in truncation on little-endian 64-bit systems and corruption (owing to
extracting top bits) on big-endian 64-bit systems. In practice the
value of chan was probably always zero on systems of the latter type as
all such FreeBSD platforms use a register-based calling convention.

Reviewed by: mav
Obtained from: CheriBSD
MFC after: 1 week
Sponsored by: DARPA, AFRL
Differential Revision: https://reviews.freebsd.org/D14673