tapsetup: add more features

[miri64]

Contribution description

This is a first step towards fixing by adding new functionalities to the tapsetup script (which I plan to use late for the common approach or at least some parts of it):

• add capability to list the bridge and all interfaces that belong to it (hopefully to replace the various get_bridge python implementation throughout the tests)
• add capability to activates forwarding on the bridge
• add capability to add addresses to the bridge
• add capability to add routes to the bridge

Testing procedure

I tested this on both Linux and FreeBSD (using the vagrant box provided at /dist/tools/vagrant/freebsd) but since the commands I used for FreeBSD are the same on OSX, it should also work there as well.

./dist/tools/tapsetup/tapsetup -c
./dist/tools/tapsetup/tapsetup -l tap0
./dist/tools/tapsetup/tapsetup -d

should list the bridge tap0 belongs to and its interfaces. If you use the name of the bridge, tapbr0 on Linux, bridge0 on FreeBSD, it should work as well.

./dist/tools/tapsetup/tapsetup -f

should create a bridge with forwarding enabled

./dist/tools/tapsetup/tapsetup -f -d

will revert that.

./dist/tools/tapsetup/tapsetup -a 2001:db8::1/48 -a fe80::1

should add the addresses 2001:db8::1/48 and fe80::1/128 to the bridge when it is created

./dist/tools/tapsetup/tapsetup -a 2001:db8::1/48 -a fe80::1 -d

should revert it.

./dist/tools/tapsetup/tapsetup -r 2001:db8::/48 fe80::2

should add a route to 2001:db8::/48 via fe80::2 and the bridge and

./dist/tools/tapsetup/tapsetup -r 2001:db8::/48 fe80::2 -d

should revert it again.

You may also try different combinations of the command.

Issues/PRs references

#14618

[benpicco]

Looks good and works as expected. I'm trusting your testing on FreeBSD.

Please squash.

[miri64]

Squashed