vrrp: change init of vrrp key in VR lookup

Type: fix

A struct that is used as a hash key was being initialized in its
declaration. On CentOS 8 this caused some hash lookups to fail.
This seems to be caused by uninitialized padding.

Use clib_memset() to initialize the key with 0's to avoid the issue.

Change-Id: I00555c201a1ab34133971313ba14f20f4e867a30
Signed-off-by: Matthew Smith <mgsmith@netgate.com>