net: systemport: Set correct RSB endian bits based on host

RSB_SWAP0 needs to match the host CPU endian, and it needs to be set
for LE and clear for BE. RSB_SWAP1 must always be cleared for SYSTEMPORT
Lite.

With these settings, we have the Receive Status Block always match the
host endian and we do not need to perform any conversion. Since there is
not necessarily a CONFIG_CPU_LITTLE_ENDIAN option defined, we test for
!CONFIG_CPU_BIG_ENDIAN which is guaranteed to be set.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>