zeromq: add PGM/EPGM support

This adds support for Pragmatic General Multicast protocol on raw
IP (PGM, RFC 3208) or UDP frames (EPGM) for use as zeromq reliable
multicast transport. The library relies on openpgm package to
implement the protocol itself.

Signed-off-by: Alexander Lukichev <alexander.lukichev@gmail.com>
Acked-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>