GCDAsyncUdpSocket: fixed wrong condition for all methods that can be used in performBlock:

Fixes #211
fixed multicast operations for IPv6
Merge pull request #214 from MeckiCologne/master

fixed multicast operations for IPv6
Podspec updated to 7.3.4
GCDAsyncSocket: fixing -Wreceiver-is-weak warnings.

Fixes #206
Merge remote-tracking branch 'upstream/master'

Conflicts:
	GCD/GCDAsyncSocket.m