3c515: fix integer overflow warning

3c515: fix integer overflow warning

clang points out a harmless signed integer overflow:

drivers/net/ethernet/3com/3c515.c:1530:66: error: implicit conversion from 'int' to 'short' changes value from 32783 to -32753 [-Werror,-Wconstant-conversion]
                new_mode = SetRxFilter | RxStation | RxMulticast | RxBroadcast | RxProm;
                         ~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~
drivers/net/ethernet/3com/3c515.c:1532:52: error: implicit conversion from 'int' to 'short' changes value from 32775 to -32761 [-Werror,-Wconstant-conversion]
                new_mode = SetRxFilter | RxStation | RxMulticast | RxBroadcast;
                         ~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~
drivers/net/ethernet/3com/3c515.c:1534:38: error: implicit conversion from 'int' to 'short' changes value from 32773 to -32763 [-Werror,-Wconstant-conversion]
                new_mode = SetRxFilter | RxStation | RxBroadcast;
                         ~ ~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~

Make the variable unsigned to avoid the overflow.

Fixes: Linux-2.1.128pre1
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>