REORG: connection: centralize the conn_set_{tos,mark,quickack} functions

REORG: connection: centralize the conn_set_{tos,mark,quickack} functions

There were a number of ugly setsockopt() calls spread all over
proto_http.c, proto_htx.c and hlua.c just to manipulate the front
connection's TOS, mark or TCP quick-ack. These ones entirely relied
on the connection, its existence, its control layer's presence, and
its addresses. Worse, inet_set_tos() was placed in proto_http.c,
exported and used from the two other ones, surrounded in #ifdefs.

This patch moves this code to connection.h and makes the other ones
rely on it without ifdefs.