libslirp: update to 4.7.0

## [4.7.0] - 2022-04-26

### Added

  - Allow disabling the internal DHCP server
  - icmp: Support falling back on trying a SOCK_RAW socket
  - Support Unix sockets in hostfwd
  - IPv6 DNS proxying support
  - bootp: add support for UEFI HTTP boot
  - New callback that supports CFI better

### Fixed

  - dhcp: Always send DHCP_OPT_LEN bytes in options
  - Fix Haiku build
  - Fix memory leak when using libresolv
  - Ensure sin6_scope_id is zero for global addresses
  - resolv: fix IPv6 resolution on Darwin
  - socket: Initialize so_type in socreate
  - Handle ECONNABORTED from recv

(nia)