vmxnet3: remove set_flag_le{16,64} helpers

It's easier to just annotate the constants as little endian types and set/clear
the flags directly.

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: Shreyas Bhatewara <sbhatewara@vmware.com>
Signed-off-by: David S. Miller <davem@davemloft.net>