util-internal: fix __func__ redefinition (netbsd)

util-internal: fix __func__ redefinition (netbsd)

==> netbsd: In file included from ../listener.c:57:0:
==> netbsd: ../util-internal.h:58:0: warning: "__func__" redefined [enabled by default]
==> netbsd:  #define __func__ EVENT____func__
==> netbsd:  ^
==> netbsd: In file included from /usr/include/amd64/types.h:39:0,
==> netbsd:                  from /usr/include/sys/types.h:45,
==> netbsd:                  from ../listener.c:30:
==> netbsd: /usr/include/sys/cdefs.h:394:0: note: this is the location of the previous definition
==> netbsd:  #define __func__ __PRETTY_FUNCTION__