iprule: add ipproto property

iprule: add ipproto property

```
config rule
	option ...
	option ipproto '17'
```

This allows handling rules which anchor to protocol number like:

`ip ru add from all ipproto udp table udp_table prior 10`

Handle ipproto as an unsigned integer.

https://www.iana.org/assignments/protocol-numbers/protocol-numbers.xhtml

Example:

config rule
	option in 'lan'
	option src '10.48.0.0/16'
	option out 'lan'
	option dest '192.168.1.144/32'
	option lookup 'main'
	option ipproto '17'

Results in

~# ip rule
0:	from all lookup local
1:	from 10.48.0.0/16 to 192.168.1.144 iif br-lan oif br-lan ipproto udp lookup main

Tested on 23.05.5 x86_64

Signed-off-by: Paul Donald <newtwen+github@gmail.com>