ARM64: Fix build break for RTL8187/RTL8192CU wifi

ARM64: Fix build break for RTL8187/RTL8192CU wifi

These drivers use an ASM function from the base
system to compute the ipv6 checksum.  These functions
are not available on ARM64, probably because nobody
has bother to write them.  The base system does have
a generic "C" version, so a simple fix is to include
the header to use the generic version on ARM64 only.

A longer term solution would be to submit the necessary
ASM function to the upstream source.

With this change, these drivers now compile without
any errors on ARM64.

Signed-off-by: Michael Zoran <mzoran@crowfest.net>