net: Use safe math macros to prevent overflows

net: Use safe math macros to prevent overflows

Replace direct arithmetic operations with macros from include/grub/safemath.h
to prevent potential overflow issues when calculating the memory sizes.

Signed-off-by: Lidong Chen <lidong.chen@oracle.com>
Signed-off-by: Alec Brown <alec.r.brown@oracle.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
Conflicts:
	grub-core/net/bootp.c
	grub-core/net/net.c

Gbp-Pq: Topic cve-2025-jan
Gbp-Pq: Name net-Use-safe-math-macros-to-prevent-overflows.patch