CVE-2022-49084

In the Linux kernel, the following vulnerability has been resolved:

qede: confirm skb is allocated before using

qede_build_skb() assumes build_skb() always works and goes straight
to skb_reserve(). However, build_skb() can fail under memory pressure.
This results in a kernel panic because the skb to reserve is NULL.

Add a check in case build_skb() failed to allocate and return NULL.

The NULL return is handled correctly in callers to qede_build_skb().