n_gsm.c: Enhancement of gsm_mux TX/RX buf allocate

n_gsm.c: Enhancement of gsm_mux TX/RX buf allocate

BZ: 28510

In LEX platform, we found huge kmalloc fail if repeated gsmld open and close
that trigged by stmd(userspace) or modem reset.

LEX memory size is 512M, only the half of Medfield.

Enhancement:
1. gsm_mux buf/txframe allocation moved to gsmld_config, according to mtu/mru of cfg
2. if encoding ==0, txframe allocate one mtu; otherwise allocate double mtu
3. if allocation size less than PAGE, use kmalloc; otherwise use vmalloc

This patch is part of the solution to TX/RX buffer allocate fail.
We also need to change mtu/mru in STMD, it should matched to N1 of AT+CMUX.
N1(Maximum Frame Size) of modem is 1509 now.

Signed-off-by: xiaojin <jin.xiao@intel.com>
Change-Id: I928f9943bce17c065e070750ccf6648d577b17ff
Reviewed-on: http://android.intel.com:8080/43942
Reviewed-by: Stoltz-douchet, OlivierX <olivierx.stoltz-douchet@intel.com>
Reviewed-by: Pillet, VincentX <vincentx.pillet@intel.com>
Reviewed-by: Xiao, Jin <jin.xiao@intel.com>
Reviewed-by: Roulliere, Pierre <pierre.roulliere@intel.com>
Reviewed-by: Liu, Chuansheng <chuansheng.liu@intel.com>
Reviewed-by: Predon, Frederic <frederic.predon@intel.com>
Reviewed-by: Lebsir, SamiX <samix.lebsir@intel.com>
Tested-by: Lebsir, SamiX <samix.lebsir@intel.com>
Reviewed-by: buildbot <buildbot@intel.com>
Tested-by: buildbot <buildbot@intel.com>