wireguard: add barrier to sync data

wireguard: add barrier to sync data

The current implmentation of the hash table is not thread-safe.
This design leads to a segfault when VPP is handling a lot of tunnels
for Wireguard, where one thread modifies the hash table and other
threads start the lookup at the same time.

This fix adds a barrier sync to the hash table access when Wireguard
adds or deletes an element.

Type: fix
Signed-off-by: Gabriel Oginski <gabrielx.oginski@intel.com>
Change-Id: Id460dfcd46ace17c7bdcd23bd9687d26cecf0a39