nbi_impl.h: remove missed prototype to fix compilation
nbi_impl.h: remove missed prototype to fix compilation

Fixes the following build error:

 In file included from ../git/src/baseboxd.cc:10:
 ../git/src/netlink/nbi_impl.h:28:39: error: use of enum 'switch_state' without previous declaration
    void switch_state_notification(enum switch_state) noexcept override;
                                        ^~~~~~~~~~~~
 ../git/src/netlink/nbi_impl.h:28:8: error: 'void basebox::nbi_impl::switch_state_notification(int)' marked 'override', but does not override
    void switch_state_notification(enum switch_state) noexcept override;
         ^~~~~~~~~~~~~~~~~~~~~~~~~

Signed-off-by: Jonas Gorski <9712c064bde5a52658fc87d6454b4956f9bf286b@bisdn.de>

bisdn/basebox,bisdn/basebox,bisdn/basebox,bisdn/basebox