Update socat to 1.7.1.3

Changelog:

security:
fixed a stack overflow vulnerability that occurred when command
line arguments (whole addresses, host names, file names) were longer
than 512 bytes.
Note that this could only be exploited when an attacker was able to
inject data into socat's command line.
Full credits to Felix Grobert, Google Security Team, for finding and
reporting this issue

(zafer)