Description of problem:
Adding several security groups as the Custom property of vNIC profile leads to error during the update of port/ creation of new port instead of successful assignment of the security groups to the port.

How reproducible:
100%

Steps to Reproduce:
1. Create 2 security groups
2. Assign their ids to the security group Custom property of the vNIC profile of ovn network separated by comma
3. Update the existing port with this vNIC profile or create a new one

Actual results:
The port is not updated (not plugged)/ not created

Expected results:
The port is updated/ created with the correct security groups.

Additional info:
Neither using comma and whitespace (A) nor just using comma (B) works - in both cases it results in incorrect parsing.
(A) Input in vNIC profile: "b291ed03-667e-46c6-8294-bd849a7f7df3, d19cdd7b-596b-4819-a2d3-cf5a9e1a9163"
REST API request body:
{
  "port" : {
    "binding:host_id" : "6a07a859-c748-4541-939c-be227498c55a",
    "mac_address" : "56:6f:f8:c9:00:00",
    "security_groups" : [ "b291ed03-667e-46c6-8294-bd849a7f7df3", " d19cdd7b-596b-4819-a2d3-cf5a9e1a9163" ]
  }
}
Error message: Port group  d19cdd7b-596b-4819-a2d3-cf5a9e1a9163 does not exist

(B) Input in vNIC profile: "b291ed03-667e-46c6-8294-bd849a7f7df3,d19cdd7b-596b-4819-a2d3-cf5a9e1a9163"
REST API request body:
{
  "port" : {
    "binding:host_id" : "6a07a859-c748-4541-939c-be227498c55a",
    "mac_address" : "56:6f:f8:c9:00:00",
    "security_groups" : [ "b291ed03-667e-46c6-8294-bd849a7f7df3", "-596b-4819-a2d3-cf5a9e1a9163" ]
  }
}
Error message: Port group -596b-4819-a2d3-cf5a9e1a9163 does not exist