selinux: nlmsgtab: add SOCK_DESTROY to the netlink mapping tables

Without this, using SOCK_DESTROY in enforcing mode results in:

  SELinux: unrecognized netlink message type=21 for sclass=32

CRs-Fixed: 1084190
Change-Id: I7862bb0fc83573567243ffa9549a2c7405b5986c
Git-commit: 2c332426b5af4edf921d064b183da76c1ae2fda6
Git-repo: https://android.googlesource.com/kernel/common/


Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>