rmnet_shs: Fix vnd delete handling

Previously shs would mark a vnd deleted by using the ep struct
passed from rmnet. However rmnet driver frees the ep struct before
the shs vnd_del notification callback. This causes shs to incorrectly
no invalidate freed vnds.

This change adds a internal struct to check for vnd match in order for
rmnet_shs to correctly invalidate vnds.

Change-Id: I1e4e86ad0ab5abe2abd569e33fba65198badb17c
Acked-by: Raul Martinez <mraul@qti.qualcomm.com>
Signed-off-by: Conner Huff <chuff@codeaurora.org>