Now that net_buf has "native" support for sys_slist_t in the form of
the sys_snode_t member, there's a danger people will forget to clear
out buf->frags when getting buffers from a list directly with
sys_slist_get(). This is analogous to the reason why we have
net_buf_get/put APIs instead of using k_fifo_get/put.
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
018198cedc