default or selected kernelversion does not have config value CONFIG_6LOWPAN_IPHC.
Result is shown for kernelversion 6.5.1

CONFIG_6LOWPAN_IPHC (not configurable)

modulename: 6lowpan_iphc.ko

configname: CONFIG_6LOWPAN_IPHC

Linux Kernel Configuration
└─>Networking support
└─>Networking options
└─>6LOWPAN_IPHC
In linux kernel since version 3.14 (release Date: 2014-03-30)  
6lowpan compression code which is shared between IEEE 802.15.4 and Bluetooth
stacks.

source code:
depends
CONFIG_NET