inpcb: retire the inpcbinfo list lock

[glebius]

Summary

With the SMR locking of inpcbs the use of this lock reduced down to the
global list and generation number. It was used only on an inpcb creation
and destruction. Use the inpcbinfo hash lock for this purpose.

[markj]

Probably the lock should be renamed to something more generic, not including "hash"?

[glebius]

In D55966#1281009, @markj wrote:

Probably the lock should be renamed to something more generic, not including "hash"?

On the next changeset in the stack lock usage is reduced mostly to the hash, as the list of all inpcbs goes away.

[pouria]

The only user of in_pcbremhash() function is now only in_pcbdrop()
should we keep it?
IMHO, since the in_pcbdrop() is small enough, maybe we should expand the in_pcbremhash() and remove it entirely.

[glebius]

In D55966#1282878, @pouria wrote:

The only user of in_pcbremhash() function is now only in_pcbdrop()
should we keep it?
IMHO, since the in_pcbdrop() is small enough, maybe we should expand the in_pcbremhash() and remove it entirely.

I haven't yet shared the entire patch queue. The in_pcbdrop() also goes away together with INP_DROPPED and this state is internalized to TCP. This depends on D56025. Once it is in main, I will rebase my branch and share missing patches.