Build warnings with nsclick and Wifi

[dgarske]

Using 24d9bf85bcad4711294113b447c8c984130849bd

./configure --disable-linuxmodule --enable-nsclick --enable-wifi && make

../elements/userlevel/fromdevice.hh:258:9: warning: private field '_was_promisc' is not used [-Wunused-private-field]
    int _was_promisc : 2;
        ^

../elements/wifi/radiotapdecap.cc:125:34: warning: taking address of packed member 'it_present' of class or structure 'ieee80211_radiotap_header' may result in an unaligned pointer value
      [-Waddress-of-packed-member]
        u_int32_t *itpp = (u_int32_t*) &th->it_present;
                                        ^~~~~~~~~~~~~~

[tbarbette]

Can you open a PR ?