Default Gateway option

[Jérôme Poulin <jeromepoulin gmail com>]

When setting a manual IP on a connection, the way the dialog box is
made, Network Manager allows a user to enter one gateway by IP,
however, in a logicial ways, a gateway should be system-wide or at
least connection-wide, not address specific.
As there is possibility to enter multiple gateway, if one enter
192.168.1.100/24 gw 0.0.0.0 then add 192.168.2.101/24 gw 192.168.2.1,
the user will get no gateway. And if the user does not enter any
gatway, the save button is grayed out without any indication why.
I don't know if there were any bug report concerning this issue of if
there's a reason about it?