tcp_hpts: move HPTS related fields from inpcb to tcpcb

[glebius]

Summary

This makes inpcb lighter and allows future cache line optimizations
of tcpcb. The reason why HPTS originally used inpcb is the TIME-WAIT
state that used to free a tcpcb, while the associated connection is
still on the HPTS ring.

[glebius]

Make tcp_in_hpts() an inline. Allows to use it outside TCPHPTS define.

[glebius]

c2a69e846fffb95271c0299e0a81e2033382e9c2