fix bridge master:slave mapping by-name
a slave may be mapped to a master by either the uuid of the master OR
the connection name of the master.
upon widget construction we'll store our current name and if it is the
one referenced by the slave we consider ourselves master of that slave.
also partially unpack the if condition so it's a bit easier on the eyes
with the newly added complexity
nmcli c add type bridge ifname br0 autoconnect yes con-name br0 stp off nmcli c add type bridge-slave autoconnect yes con-name enp4s0 ifname enp4s0 master br0
kcm correctly shows enp4s0 as slave of br0
Reviewed By: jgrulich
Differential Revision: https://phabricator.kde.org/D23125