network/dhcpv4: add ability to use BOOTP (#34888)

BOOTP can be used to sign a static IP to clients. Instead of using the
four message exchange, and Option 53 (DHCP Message Type) there is only a
two message exchange.

Add the following network option to enable BOOTP:

[DHCPv4]
BOOTP=yes

This will allow a two message request / reply sequence that doesn't
require DHCP message types.

Fixes: #34885