drivers: rmnet_shs: Fix DEBUG_LIST/spinlock error

Previously during SSR the nodes were not cleaned up on reinit
old nodes would be cleanup incorrectly as reinit would invalidate
their contents. This change correctly does a clean up on old
nodes during SSR to fix this.

Spinlock deadlock was occuring between shs wq and rx context
when spinlock_irqsave was not being called.
Change all spinlock calls to spinlock_irqsave.

CRs-Fixed: 2340672
Change-Id: I3bc3708e8f900738b1835a0d164ff69c138846ca
Acked-by: Raul Martinez <mraul@qti.qualcomm.com>
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>