net: Simplify the calculation of variables

Fix the following coccicheck warnings:

 ./net/ipv4/esp4_offload.c:288:32-34: WARNING !A || A && B is
equivalent to !A || B.

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Zhong <abaci-bugfix@linux.alibaba.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>