Handle IPv6 hosts as Socks destination

[FrankTaylorLieder]

(Note: I could not find docs on how to contribute to this repo, let me know if there is a process to follow.)

This change fixes an issue when accessing IPv6 services through the SOCKS proxy using their IP address rather than hostname:

• The IP address is passed over to the SOCKS proxy as type ATYP=0x03 (Domain name) instead of ATYP=0x04 (Address).
• The remote end therefore tries to DNS resolve the address, which fails.

The root cause is:

• The target URI is of the form http://[2001:db8::1]:8080.
• The proxy extracts the host part of the URI and gets back [2001:db8::1]. (src/client/legacy/connect/proxy/socks/v4/mod.rs:133)
• It attempts to parse this as an address and fails, so assumes its a domain name. Incorrect.
• This is not a valid IPv6 address due to the square brackets (they are part of the URI encoding of IPv6 addresses). These need to be stripped to make a valid IPv6 address.

Fix:

• Strip any square brackets from the host part of the URI.
• There will never be square brackets in valid domain names or IPv4 addresses.