ifconfig(8): Add kld mappings for ipsec/enc

Additionally, providing mappings makes the comparison for already loaded
modules a little more strict. This should have been done at initial
introduction, but there was no real reason- however, it proves necessary for
enc which has a standard enc -> if_enc mapping but there also exists an
'enc' module that's actually CAM. The mapping lets us unambiguously
determine the correct module.

Discussed with: ae
MFC after: 4 days