net/sfc: fix flow control settings on port start

net/sfc: fix flow control settings on port start

efx_phy_adv_cap_set() sets all advertised phy capabilities including
pause capabilities which are also configured using efx_mac_fcntl_set().

If we set speed and autonegotiation capabilities only, we should
preserve already configured pause capabilities.

Fixes: d23f3a89ab54 ("net/sfc: support link speed and duplex settings")
Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>
Reviewed-by: Andrew Lee <alee@solarflare.com>