device/lms: fix: 'trx_vty.h' header requires C linkage
device/lms: fix: 'trx_vty.h' header requires C linkage

Otherwise, the linker fails to produce osmo-trx-lms binary:

  LMSDevice.cpp:493: undefined reference to
    `get_value_string(value_string const*, unsigned int)'

  LMSDevice.cpp:237: undefined reference to
    `osmo_panic(char const*, ...)'

Change-Id: I2fef166c13136af7b7aaa744d39427d76ad11769
Fixes: OS#4828

osmocom/osmo-trx,osmocom/osmo-trx,osmocom/osmo-trx,osmocom/osmo-trx