Merge branch 'ipv4-null-cmp'

Ian Morris says:

====================
ipv4: coding style - comparisons with NULL

Per the suggestion of Joe Perches, attached is a patch which aligns the
coding style in ipv4 for comparisons with NULL.

The code uses multiple different styles when comparing with NULL (I.e.
x == NULL and !x as well as x != NULL and x). Generally the latter form
is preferred in netdev and so this changes aligns the code to this style.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>