Add @Nullable to Object#equals()

This is a partial cherry-pick of change:
I5eedb571c9d78862115dfdc5dae1cf2a35343580

for connectivity classes.

Bug: 170883422
Test: m
Merged-In: I5eedb571c9d78862115dfdc5dae1cf2a35343580
Change-Id: I7dc661863b73f4198ddb4f3a1566583d0f07db3c

framework/src/android/net/ProxyInfo.java

@@ -275,7 +275,7 @@ public class ProxyInfo implements Parcelable {
     }
 
     @Override
-    public boolean equals(Object o) {
+    public boolean equals(@Nullable Object o) {
         if (!(o instanceof ProxyInfo)) return false;
         ProxyInfo p = (ProxyInfo)o;
         // If PAC URL is present in either then they must be equal.