cli: don't reset default values in interactive add
Since commit 40032f46 ('cli: fix resetting values via property alias'), nmcli sets NULL properties during interactive add (nmcli -a connection add) when the user leaves the field blank. This can lead to an invalid connection for properties that can't be empty like infiniband.transport-mode; they should be left to the default value in case of no value entered.
Fixes: 40032f46 ('cli: fix resetting values via property alias') Fixes-test: @inf_create_port_novice_mode https://bugzilla.redhat.com/show_bug.cgi?id=2053603