Test that an SA Can be Updated with a Mark

This test verifies that an SA, in this case created
with ALLOCSPI, can be subsequently updated with UPDSA
to add a Mark value.

-Add Mark attribute support in DeleteSaInfo, so now we
 can delete SAs that have marks.
-Add the proto field in AllocSpi; otherwise, when an
 SA is added, an UNSPEC proto is treated separately from
 an explicitly AF_INET/AF_INET6 SA, which seems to be
 broken behavior we wish to avoid.
-Add a test that calls ALLOCSPI without a mark, then
 later updates the SA and adds a mark. Because the original
 mark is unset, the new mark is masked off during the match,
 but it is applied to the SA as part of the update.

Bug: 66467511
Test: run_net_test.sh xfrm_test.py
Change-Id: Ib7c95da0f2fc11582edd960c845dc74da5d75095