qlnxe: Let ether_ioctl() handle SIOCSIFADDR ioctl

Since the change [1], the init routine qlnx_init() works as intended.
Let ether_ioctl() handle SIOCSIFADDR to simplify the code.

Combined with the change [1], this shall be a better fix for PR 287445.

[1] c10e6bc0f007 qlnxe: Avoid reinitializing the interface when it is already initialized

PR: 287445
Reviewed by: kbowling
MFC after: 5 days
Differential Revision: https://reviews.freebsd.org/D54888