Revert "net: rtnetlink: add NLM_F_BULK support to rtnl_fdb_del"

This reverts commit 4b714092 which is
commit 9e834259 upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: I065c84bd7cc13eb97aacf866af01a8b5c93d3d64
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>