Ignore the interfaces defined in IGNORED_INTERFACES

In getInterfaces(), ignore the interfaces if it is in the environment
IGNORED_INTERFACES.

Tested: Verify the interfaces are ignored by phosphor-networkd if it's
        defined in the environment configs.

Signed-off-by: Lei YU <yulei.sh@bytedance.com>
Change-Id: I159e4e8613c7795d371beef0b1c1131586a5126d
diff --git a/util.cpp b/util.cpp
index ee76cc3..6cc42d1 100644
--- a/util.cpp
+++ b/util.cpp
@@ -391,12 +391,14 @@
 
     AddrPtr ifaddrPtr(ifaddr);
     ifaddr = nullptr;
+    const auto& ignoredInterfaces = internal::getIgnoredInterfaces();
 
     for (ifaddrs* ifa = ifaddrPtr.get(); ifa != nullptr; ifa = ifa->ifa_next)
     {
         // walk interfaces
         // if loopback ignore
-        if (ifa->ifa_flags & IFF_LOOPBACK)
+        if (ifa->ifa_flags & IFF_LOOPBACK ||
+            ignoredInterfaces.find(ifa->ifa_name) != ignoredInterfaces.end())
         {
             continue;
         }