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

This reverts commit b58a295d 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: I2361b94c8f658b3ec2be984682e7f9780f2e3ac3
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>