lib.yang.data: parse defaults of nested leaves
lib.yang.data: parse defaults of nested leaves

This fixes a bug where the YANG parser would not return default values
for leaves which nested in containers left unspecified in the
configuration.

eugeneia/snabb,eugeneia/snabb,Igalia/snabb,eugeneia/snabb,eugeneia/snabb,Igalia/snabb,SnabbCo/snabbswitch,eugeneia/snabb,eugeneia/snabb,snabbco/snabb,eugeneia/snabb,eugeneia/snabb,snabbco/snabb,Igalia/snabb,snabbco/snabb,snabbco/snabb,snabbco/snabb,snabbco/snabb,snabbco/snabb,Igalia/snabb,SnabbCo/snabbswitch,Igalia/snabb,SnabbCo/snabbswitch,Igalia/snabb,snabbco/snabb,Igalia/snabb,Igalia/snabb,SnabbCo/snabbswitch