Now, ifa_dev is only set in inet_alloc_ifa() and never
NULL after ifa gets visible.

Let's remove the unneeded NULL check for ifa->ifa_dev.
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20240809235406.50187-4-kuniyu@amazon.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>