Add antispoofing option for CSR

Add support for a 'disable_anti_spoofing' option. If set, a second
option 'sec_group_svc_VM_name' will be enabled which lists security
groups that do not have Neutron anti-spoofing rules applied. Together
the two allow disabling of anti-spoofing rules on a per-port basis as
needed for service VMs.

Code contributed by Ly Loi and Nabil Maadarani.

Partial-Bug: #1343401