XfrmController.h - fix a virtual method call from destructor warning

Fixes:
  system/netd/server/XfrmController.h:67:29: error: Call to virtual method 'XfrmSocket::close' during destruction bypasses virtual dispatch [clang-analyzer-optin.cplusplus.VirtualCall,-warnings-as-errors]
      virtual ~XfrmSocket() { close(); }
                              ^
  system/netd/server/XfrmController.cpp:630:5: note: Taking false branch
      if (!isOk(ret)) {
      ^
  system/netd/server/XfrmController.cpp:636:5: note: Taking true branch
      if (!isOk(socketStatus)) {
      ^
  system/netd/server/XfrmController.cpp:638:16: note: Calling implicit destructor for 'XfrmSocketImpl'
          return socketStatus;
                 ^
  system/netd/server/XfrmController.cpp:638:16: note: Calling '~XfrmSocket'

Test: builds
Bug: 155351989
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I992c9899d9f9fc6a45fac28cad46db6331436099