Modernize codebase by replacing NULL with nullptr

Fixes -Wzero-as-null-pointer-constant warning.

Test: m
Bug: 68236239
Change-Id: I226a0599db4f7c3557e55cade7869d00bd314949
diff --git a/server/NetworkController.cpp b/server/NetworkController.cpp
index 7e22ad2..b722c76 100644
--- a/server/NetworkController.cpp
+++ b/server/NetworkController.cpp
@@ -387,7 +387,7 @@
 }
 
 int NetworkController::createPhysicalOemNetwork(Permission permission, unsigned *pNetId) {
-    if (pNetId == NULL) {
+    if (pNetId == nullptr) {
         return -EINVAL;
     }
 
@@ -731,7 +731,7 @@
 
 Network* NetworkController::getNetworkLocked(unsigned netId) const {
     auto iter = mNetworks.find(netId);
-    return iter == mNetworks.end() ? NULL : iter->second;
+    return iter == mNetworks.end() ? nullptr : iter->second;
 }
 
 VirtualNetwork* NetworkController::getVirtualNetworkForUserLocked(uid_t uid) const {
@@ -743,7 +743,7 @@
             }
         }
     }
-    return NULL;
+    return nullptr;
 }
 
 Permission NetworkController::getPermissionForUserLocked(uid_t uid) const {