[client] -R http recv() read until close (Jonathan Schulz)

[client] -R http recv() read until close (Jonathan Schulz)

Applied patch from Jonathan Schulz to ensure that the fwknop client reads all
data from a remote webserver when resolving the client IP address in -R mode.
Jonathan indicated that some webservers would transfer HTTP headers and data
separately, and a single recv() would therefore fail to get the necessary IP
information.