Nftables: Support xt_MASQUERADE compatibility target.

Added:
- `xt_MASQUERADE` target extension.
    Masq can dynamically rewrites the packet's source IP
    to match the outgoing interface's primary IP.
- Masq Revision 0 ABI.
- Unit and syscall tests.

Ref: net/netfilter/xt_masquerade.c
PiperOrigin-RevId: 965062213