CA-96950: Fix HIMN bridge name if needed

Previously, the bridge name used for the Host Internal Management Network
(HIMN) was usually xapi0, i.e. a normal name in the xapi* range. Now, the HIMN
has a special bridge name ("xenapi").

This commit ensures that the new name is used on existing HIMNs.

Signed-off-by: Rob Hoes <rob.hoes@citrix.com>
Merge pull request #1081 from robhoes/ca96950

CA-96950: Fix HIMN bridge name if needed