Kernel 4.14 and later supports dev_scratch for network
buffer which can be used to store data in a nbuf in the
format unsigned long.
Add APIs:
1) qdf_nbuf_is_dev_scratch_supported
2) qdf_nbuf_get_dev_scratch
3) qdf_nbuf_set_dev_scratch
Change-Id: I2a72d369bb53f8f86d4bcee3cf6d13f5e4aff57f
CRs-Fixed: 2313270