Remove vestiges of WinIP library.

This was an old library removed in r2811 and r2812, of which a few
traces remained.

I don't know the purpose of this in nbase_misc.c:
  if(sd != 501) // Hack related to WinIP Raw Socket support
    ioctlsocket (sd, FIONBIO, &one);

tcpip.h

@@ -536,9 +536,7 @@ void broadcast_socket(int sd);
 int recvtime(int sd, char *buf, int len, int seconds, int *timedout);
 
 /* Sets a pcap filter function -- makes SOCK_RAW reads easier */
-#ifndef WINIP_H
 void set_pcap_filter(const char *device, pcap_t *pd, const char *bpf, ...);
-#endif
 
 #endif /*TCPIP_H*/