scripts/mosh: Allow IO::Socket::INET6 as an alternative to IO::Socket::IP

Some systems have IO::Socket::INET6 preinstalled, so we might as well
accept either.

Signed-off-by: Anders Kaseorg <andersk@mit.edu>

man/mosh.1

@@ -123,7 +123,8 @@ Synonym for \-\-predict=never
 .TP
 .B --family=\fIFAMILY\fP
 Force the use of a particular address family, which defaults to `inet'
-(IPv4), and can also be `inet6' (IPv6; requires IO::Socket::IP).
+(IPv4), and can also be `inet6' (IPv6; requires IO::Socket::IP or
+IO::Socket::INET6).
 
 .TP
 .B -4