End the process after one result in case -l is not given
and destination address is unicast.
Reduces singleshot execution time from timeout seconds to around 150ms.

resolves #2184

inet_pton() doesn't set errno on regular parse errors, so using perror()
doesn't make sense (and we avoid a confusing "Success" message).

gluon-neighbour-info: improve verbosity on wrong cli parameters

The timeout was calculated incorrectly (in each iteration the span between
the start time and the current time was substracted from the timeout
again), and would often become negative, causing warnings in the kernel
log.

sse-multiplex likes to get the header as fast as possible.

error() is a glibc specific function and should not be used in
code meant to be portable.

This is a simple client for gluon-announced.