vhost-net: check the support of mergeable buffer outside the receive loop
vhost-net: check the support of mergeable buffer outside the receive loop

No need to check the support of mergeable buffer inside the recevie
loop as the whole handle_rx()_xx is in the read critical region.  So
this patch move it ahead of the receiving loop.

Signed-off-by: Jason Wang <808efd45667dbd241e4e026b5673172419ecb43e@redhat.com>
Signed-off-by: Michael S. Tsirkin <255103e50249e3d658441816e0597170ebfc16ef@redhat.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs