cxgbe(4): Do not issue an L1CFG command from a VF.

It is pointless to attempt an operation that is not permitted. It spams
the firmware devlog with "insufficient caps" errors that distract from
real errors.

78 2463625358 ERR CORE insufficient caps to process mailbox cmd: pfn 0x0 vfn 0x1; r_caps 0x86 wx_caps 0x82 required r_caps 0x81 w_caps 0x5

MFC after: 1 week
Sponsored by: Chelsio Communications

(cherry picked from commit d72db09005e53160d6c89b5221169efaac74cd55)