Use "hairpin mode" by-default / more often

[robmry]

Description

From @akerouanton's review comment #47871 (comment) ...

Maybe we can now make 'hairpin mode' the default, or at least use it more often?

• It was initially introduced in moby/libnetwork@acfac0b
• Then, libnet devs realized the netlink message used was too new for some kernels supported at that time, as can be seen in this comment: Use sysfs to set hairpin mode libnetwork#412 (comment)
• netlink uses the const IFLA_BRPORT_MODE, which was introduced by this commit torvalds/linux@c75ea26, which was first released in v3.8.
• RHEL 8.10 uses 4.18 -- the oldest kernel we've to support. So we should be good by now.
• But we'd need to double-check if this would introduce new issues, etc...