Update header unpack formatting to fix ICMPv6 requests

[dkaplan1]

The current header struct format bbHHh will cause ICMPv6 response types to be interpreted wrong, which results in a timeout. Since ICMP6_ECHO_REPLY = 129

aioping/aioping/__init__.py

Line 101 in 45102cb

ICMP6_ECHO_REPLY = 129

we need to unpack the type as unsigned (ref) or else the type will never match (129 vs -127)

aioping/aioping/__init__.py

Line 166 in 45102cb

if type != ICMP_ECHO_REPLY and type != ICMP6_ECHO_REPLY:

.