Revert "net: gem: Disable broadcast setting"

This reverts commit eafdcda4.

The main reason is that QEMU is using BOOTP protocol which is sending DHCP
Offer to a broadcast address that's why it can't be disabled.
DHCP protocol has no issue because it returns directly to client MAC
address.
Both of these options are described in RFC951
(https://datatracker.ietf.org/doc/html/rfc951#section-4

)

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>
Link: https://lore.kernel.org/r/fc5f5e2aeca77847ed4ca6a263890375ab9f5163.1642162545.git.michal.simek@xilinx.com