cxgbe: fix enabling lro & rxtimestamps

A recent change caused iq flags, like LRO, to be set before
init_iq(). However, init_iq() clears those flags, so they
became effectively impossible to set. This change moves
the initializion of these flags to after the call to init_iq().
This fixes LRO.

Differential Revision: https://reviews.freebsd.org/D30460
Reviewed by: np, rrs
Sponsored by: Netflix
Fixes: 43bbae19483fbde0a91e61acad8a6e71e334c8b8

(cherry picked from commit df8437a93dd5268e5bfd06411c01a5cbdb38c6ac)