A htt message arrived after ipa context is freed as part of
deinitialization which was dereferenced by event handler
assigned to pdev->ipa_uc_op_cb, resulting in crash.
To fix this, cdp function is called during deinit to
deregister pdev->ipa_uc_op_cb and assign it NULL. Also, adding
NULL check in wlan_ipa_uc_op_cb. Also, registering ipa_uc_op_cb
after work is created so as to not hit condition where work is
scheduled before creation.
Change-Id: Ib79136b1122625079d8173a401dba5516126c621
CRs-Fixed: 2794663
bbe449f218