mac80211: Allocate new mesh path and portal tables before taking locks

It is unnecessary to hold the path table resize lock while allocating a
new table.  Allocate first and take lock later.  This resolves a
soft-lockup:

[  293.385799] BUG: soft lockup - CPU#0 stuck for 61s! [kworker/u:3:744]
(...)
[  293.386049] Call Trace:
[  293.386049]  [<c119fd04>] do_raw_read_lock+0x26/0x29
[  293.386049]  [<c14b2982>] _raw_read_lock+0x8/0xa
[  293.386049]  [<c148c178>] mesh_path_add+0xb7/0x24e
[  293.386049]  [<c148b98d>] ? mesh_path_lookup+0x1b/0xa6
[  293.386049]  [<c148ded5>] hwmp_route_info_get+0x276/0x2fd
[  293.386049]  [<c148dfb6>] mesh_rx_path_sel_frame+0x5a/0x5d9
[  293.386049]  [<c102667d>] ? update_curr+0x1cf/0x1d7
[  293.386049]  [<c148b45a>] ieee80211_mesh_rx_queued_mgmt+0x60/0x67
[  293.386049]  [<c147c374>] ieee80211_iface_work+0x1f0/0x258
(...)

Signed-off-by: Javier Cardona <javier@cozybit.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>