Revert "espintcp: remove encap socket caching to avoid reference leak"

This reverts commit e4cde54b which is
commit 02836368 upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: I05ba7cd52d70dad7ccd570cfad6daec79c5ca791
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>