[bhyve] Pass a complete string of parameters to network backends

[afedorov]

Summary

These changes are needed to integrate the Netgraph backend. See discussion: https://reviews.freebsd.org/D24620

I also think passing all the arguments to the backend can be useful in the future.

Test Plan

Test various combinations with mac and mtu options:

• -s X:Y,virtio-net,tap,mtu=X,mac=XXXXXX
• -s X:Y,virtio-net,valeN:M,mtu=X,mac=XXXXXX
• -s X:Y,e1000,tap,mtu=X,mac=XXXXXX
• -s X:Y,e1000,valeN:M,mtu=X,mac=XXXXXX

And without options:

• -s X:Y,virtio-net,tap
• -s X:Y,virtio-net
• -s X:Y,e1000,tap
• -s X:Y,e1000

[vmaffione]

usr.sbin/bhyve/net_backends.c

759 ↗

(On Diff #71460)

Please return -1. The caller will check errno if needed.
I know below (EINVAL) is returned, but I see that as a leftover that should be removed.

usr.sbin/bhyve/pci_e82545.c

2284 ↗

(On Diff #71460)

optscopy may be a better name?

[afedorov]

• Fix the indicated issues.

@vmaffione , if you have no objection, can I commit these changes?

[vmaffione]

Have you tested the case with no arguments, e.g.:

-s X:Y,virtio-net,tap1

?
After that, please go ahead and commit.
Thanks.

[afedorov]

• Free optscopy early.
• While I'm here, fix a memory leak in e1000 frontend.