tftp: convert IPv6-mapped IPv4 addresses to IPv4

If we receive IPv4 addresses mapped to IPv6, convert them back to IPv4
so that mapping scripts which use \i behave sanely.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
tftpd: allow IPv4/6-specific remapping rules

Allow remapping rules to be conditional on IPv4 vs IPv6.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
tftpd.8: document IPv6 handling in remapping rules

Document the "4" and "6" conditionals as well as how \i and \x handle
IPv6 addresses.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
tftp: drop "inline" from definition of usage()

It is pointless and newer gcc say it is a lose.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>