remove some unused functions

Identified with `cppcheck --enable=unusedFunction .`.

 - GetSendBufferSize()'s last use removed in
   991955ee81
 - SetPort()'s last use removed in
   7e195e8459
 - GetfLargeWorkInvalidChainFound() was introduced in
   e3ba0ef956 and never used

src/netaddress.h

@@ -148,7 +148,6 @@ class CService : public CNetAddr
         CService(const struct in_addr& ipv4Addr, unsigned short port);
         CService(const struct sockaddr_in& addr);
         void Init();
-        void SetPort(unsigned short portIn);
         unsigned short GetPort() const;
         bool GetSockAddr(struct sockaddr* paddr, socklen_t *addrlen) const;
         bool SetSockAddr(const struct sockaddr* paddr);