Ok looking in DMESG I found this:
[ 3.789865] cxgb4 0000:15:00.4: Direct firmware load for cxgb4/t4-config.txt failed with error -2
[ 4.541838] cxgb4 0000:15:00.4: Successfully configured using Firmware Configuration File "Firmware Default", version 0x0, computed checksum 0x0
[ 4.737838] cxgb4 0000:15:00.4: max_ordird_qp 21 max_ird_adapter 387072
[ 4.871312] cxgb4 0000:15:00.4: 98 MSI-X vectors allocated, nic 16 per uld 16
[ 4.871320] cxgb4 0000:15:00.4: 32.000 Gb/s available PCIe bandwidth (5 GT/s x8 link)
[ 4.907195] cxgb4 0000:15:00.4 eth0: eth0: Chelsio T420-CR (0000:15:00.4) 1G/10GBASE-SFP
[ 4.907445] cxgb4 0000:15:00.4 eth1: eth1: Chelsio T420-CR (0000:15:00.4) 1G/10GBASE-SFP
[ 4.907514] cxgb4 0000:15:00.4: Chelsio T420-CR rev 2
[ 4.907515] cxgb4 0000:15:00.4: S/N: PT32120701, P/N: 110112040E0
[ 4.907516] cxgb4 0000:15:00.4: Firmware version: 1.23.4.0
[ 4.907518] cxgb4 0000:15:00.4: Bootstrap version: 255.255.255.255
[ 4.907519] cxgb4 0000:15:00.4: TP Microcode version: 0.1.9.4
[ 4.907520] cxgb4 0000:15:00.4: No Expansion ROM loaded
[ 4.907521] cxgb4 0000:15:00.4: Serial Configuration version: 0x4271203
[ 4.907522] cxgb4 0000:15:00.4: VPD version: 0x1
[ 4.907523] cxgb4 0000:15:00.4: Configuration: RNIC MSI-X, Offload capable
[ 4.913430] cxgb4 0000:15:00.4 ens1f4: renamed from eth0
[ 4.930056] cxgb4 0000:15:00.4 ens1f4d1: renamed from eth1
But still unable to get link between chelsio and switch.
I've tried CISCO clone SFP+ as well as UNIFI clone SFP+ from ADDON.
I just got some geniune Cisco SFP-10G-SR SFP's so I'll try those next I guess.