net/smc: support max connections per lgr negotiation

Support max connections per lgr negotiation for SMCR v2.1,
which is one of smc v2.1 features. Server makes decision for
the final value of max conns based on the client preferred
max conns and self-preferred max conns. Here use the minimum
value of client preferred max conns and server preferred max
conns.

Client                                     Server
     Proposal(max conns(client preferred))
     ------------------------------------>

     Accept(max conns(accepted value))
accepted value=min(client preferred, server preferred)
     <-----------------------------------

     Confirm(max conns(accepted value))
     ----------------------------------->

Signed-off-by: Guangguan Wang <guangguan.wang@linux.alibaba.com>
Reviewed-by: Tony Lu <tonylu@linux.alibaba.com>
Reviewed-by: Jan Karcher <jaka@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>