Dual NICs doesn't mean double bandwidth

It's very unlikely that bonding your interfaces will result in a speed increase. Typically, even if you bond the interfaces successfully AND configure the switch to support the etherchannel), then you will still find that only one interface in the bond is used
for each pair of source/destination TCP/UDP session.

So if you copy a 10Gb file from one server, then kick off another 10Gb copy to that server, assuming that you also have session based bonding, you'll see both cards maxed out. But crucially, the first
copy will only consume ONE network card, not both.

This is certainly the case with Cisco's etherchannel. In fact, Cisco's etherchannel isn't even session based, it's source/destination based, so in my example above, you wouldn't even get a speed increase - your second copy would have to be to a completely different
server before you saw both cards used. Perhaps you have a better switch that allows for the port channel to utilise both cards simultaneously in one TCP/UDP session but it would require some pretty funky arp/MAC manipulation and I have no idea if the bonding
module in linux supports that.

As for you, you're using a bog-standard home router, so switch-side support is out of the question here, meaning that your options are further limited (see the first article lined to below, where you will note that you now cannot use the best mode for link
aggregation, mode 4).

If you're determined to go ahead with this, I found this five year old article which
still seems relevant. Additionally, this three year old article covers the same ground.

From: http://askubuntu.com/questions/32179/two-ethernet-ports-on-motherboard-how-can-i-get-double-the-bandwidth