Just looking at the hashtable entry of 'updelay' and 'downdelay' options
is wrong, we have to inspect their values to check if they're
actually enabled or not.

Otherwise bond connections with valid settings will fail
when created:

$ nmcli c add type bond ifname bond99 bond.options miimon=0,updelay=0,mode=0
Error: Failed to add 'bond-bond99' connection: bond.options: 'updelay' option requires 'miimon' option to be set

Also add unit tests.

https://bugzilla.redhat.com/show_bug.cgi?id=1805184

Fixes: d595f784 ('libnm: add libnm/libnm-core (part 1)')