modules: fix freebsd32_modstat on big endian platforms

modules: fix freebsd32_modstat on big endian platforms

The layout of modspecific_t on both little endian and big endian are as
follows:
|0|1|2|3|4|5|6|7|
+-------+-------+
|uintval|       |
+-------+-------+
|ulongval       |
+-------+-------+

For the following code snippet:
        CP(mod->data, data32, longval);
        CP(mod->data, data32, ulongval);
It only takes care of little endian platforms that it truncates the
highest 32bit automatically. However on big endian platforms it takes
the highest 32bit instead. This eventually returns a garbage syscall
number to the 32bit userland.

Since modspecific_t's usage currently is for the use of syscall modules,
we only initialize modspecific32_t with uintval. Now on both BE and LE
64-bit platforms it always pick up the first 4 bytes.

Sponsored by:	Juniper Networks, Inc.
Reviewed by:	markj
Differential Revision:	https://reviews.freebsd.org/D40814
MFC after:	1 week